Field of the invention The present invention relates to an industrially viable and advantageous process for the preparation of Λ/-(((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methyl)pro pionamide, generally known as Tasimelteon, or of intermediates useful in the synthesis thereof; the invention also relates to some intermediate salts obtained in the process.

State of the art R,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methyl)prop ionamide, also known as Tasimelteon, is a drug approved for the treatment of non-24-hour sleep-wake disorder (generally referred to simply as "non-24").

Non-24 is a serious, debilitating, chronic disorder that occurs when individuals are unable to synchronize their endogenous circadian clock to the 24-hour light-dark cycle. The majority of reported cases of non-24 occurs in blind patients with no conscious perception of light. As a result of light information failing to reach the suprachiasmatic nucleus (SCN) to synchronize the clock and its outputs, the pacemaker may revert to its endogenous non-24-hour period. The result of this lack of entrainment is the gradual shifting of the endogenous rhythm as compared to the social/environmental 24-hour clock. The progressive shifting of the rhythm also produces a cyclical remission during which alignment will be achieved every 1 to 16 months depending on the period of the endogenous clock. In non-24, the timing of physiology and behaviour that is controlled by the circadian system (e.g. the timing of melatonin and Cortisol production, the core body temperature rhythm, metabolic processes, the sleep-wake cycle, and alertness and performance patterns) becomes desynchronized from the 24-hour day, which has serious consequences on the daily functioning of the patient. Non-24 is associated with significant clinical symptoms which are often mistakenly diagnosed as related to insomnia, rather than as a result of a non-entrained circadian clock, often leading to inappropriate therapeutic interventions. For some totally blind individuals, the sleeplessness and daytime somnolence that result from being non-entrained have profound impacts on their social and occupational lives and can be considered the most disabling aspects of their blindness. The ultimate goal in treating individuals with non-24 is to entrain their circadian clock with the 24-hour day so that the timing of their physiology and behaviour is synchronized appropriately with the 24-hour social day. Onset of non-24 can occur at any age, from birth onward, and usually coincides with or follows shortly after the total loss of light perception or loss or surgical removal of the eyes. The risk of developing non-24 ultimately depends on the risk of complete loss of circadian photoreceptive function rather than on the cause of blindness; any ocular disorder that abolishes light-dark input to the circadian pacemaker and prevents entrainment to the light-dark cycle can lead to non-24. Eye disorders that damage the ganglion cell layer (e.g., glaucoma), affect the optic nerve (e.g., retinopathy of prematurity), or cause removal of the eye entirely (e.g., retinoblastoma, trauma) are more likely to result in total blindness, prevent circadian entrainment, and therefore increase the likelihood of non-24.

Tasimelteon, depicted below, is a circadian regulator that resets the master body clock in the suprachiasmatic nucleus.

Tasimelteon

It is a Dual Melatonin Receptor Agonist (DMRA) with selective agonist activity at the MT1 and MT2 receptors believed to act in the suprachiasmatic nucleus.

Tasimelteon and other similar compounds were first described in international patent application WO 98/25606 A1. The process described therein entails, as key steps, a palladium catalysed cyclization of (1 R,2R)-2-(2,3-dihydrobenzofuran-4-yl)propenoyl)-2,10- camphorsultam; the reaction of ((1 R,2R)-2-(2,3-dihydrobenzofuran-4- yl))cyclopropanecarboxaldehyde with hydroxylamine hydrochloride; and the final reaction between ((1 R,2R)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine and propionyl chloride, according to the following scheme:

Tasimelteon

On industrial scale, the use of this synthesis route has several drawbacks caused by the poor selectivity of the propionylation step, the chromatographic separation required to recover the product, the high cost of the Oppolzer's camphor sultam and the known problems concerning the use of 1 -methyl-3-nitro-1 -nitrosoguanidine, a precursor of diazomethane, a compound known for its explosiveness by shock, friction or heat and its high toxicity by inhalation. An alternative process for the preparation of Tasimelteon has been described in international application WO 2014/091 167 A1. According to this document, Tasimelteon in the form of a racemic mixture can be prepared by reacting a cyclopropyltrifluoroborate with 4- bromo-2,3-dihydrobenzofuran, according to the following scheme:

(+)-Tasimelteon A disadvantage associated with the latter synthetic pathway is that in converting a racemic starting material into an enantiomerically pure end product (as in the case of Tasimelteon), a maximum yield of 50% can be reached, therefore their application on industrial scale may be considered hardly feasible to the extent that at least 50% of the final product (or a direct precursor thereof) is actually wasted. A further synthetic approach for the preparation of Tasimelteon including, as key step, an epoxidation of 4-vynil-2,3-dihydrobenzofuran, and an optical resolution of a trans-2-(2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine by means of (+)-camphorsulfonic acid has been described in the Journal of Chemical Research (2016), 40, 667-669.

A further procedure for the stereoselective preparation of Tasimelteon has been described in international application WO 2015/123389 A1. The synthetic path disclosed therein includes an asymmetric cyclopropanation in the presence of a (salen)ruthenium(ll) complex followed, in the final step, by the reaction of ((1 R,2R)-2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine with propionyl chloride, according to the scheme depicted below.

Enantiomerically Enantiomerically

mixture

lamine

A drawback of this route is that the asymmetric cyclopropanation of 4-vynil-2,3- dihydrobenzofuran and the following optical purification of the desired diastereomer by means of (+)-dehydroabietylamine are carried out at a relatively late stage. As a consequence of that, and taking into account that the enantiomer of Tasimelteon can be hardly removed from the final product by means of crystallization, any even partial racemisation occurring during the conversion of this purified salt into the final product may adversely affect the enantiomeric purity of the desired product and, thus, its compliance with specifications.

Aim of the present invention is to provide a chemical method to prepare Tasimelteon or intermediates useful in the synthesis thereof, characterized by high yields and levels of stereocontrol, and providing the desired compounds with a purity appropriate for the use in pharmaceuticals.

Summary of the invention

These objectives were achieved with the present invention, which, in a first aspect thereof, relates to a process for the preparation of a diastereomerically and enantiomerically pure propionamide of formula (4): said process comprising the following synthetic operations: a) preparing a diastereomerically and enantiomerically pure cyclopropylmethanamine (3) or a diastereomerically and enantiomerically pure salt of the cyclopropylmethanamine (3) with a chiral Bransted acid: b) treating said pure cyclopropylmethanamine (3) or said salt with a chiral Br0nsted acid with 1 -(1 /-/-imidazol-1 -yl)propan-1 -one (2):

to yield compound of formula (4).

In further aspects thereof, the present invention relates to specific intermediate compounds as well as to their use for preparing compound of formula (4).

Detailed description of the invention

All terms used in the present application, unless otherwise indicated, must be interpreted in their ordinary meaning as known in the technical field. Other more specific definitions for some terms used in the present application are given below and are intended to be applied uniformly to the entire description and claims, unless otherwise indicated.

In general, the nomenclature used in this application is based on AUTONOM™ v.4.0, a Beilstein Institute computerized system for the generation of lUPAC systematic nomenclature. If there is a discrepancy between a depicted structure and a name given to that structure, the depicted structure should be considered correct. Furthermore, if the stereochemistry of a structure or a portion of a structure is not indicated with, for example, bold or dashed lines, the structure or portion of the structure has to be interpreted as encompassing all existing stereoisomers of it.

The compounds prepared by the processes of the present invention may have one or more stereogenic centers and may exist and may be used or isolated in enantiomerically pure forms, as enantiomeric enriched mixtures as well as in diastereomerically pure forms or as diastereomeric enriched mixtures. It is to be understood that the processes of the present invention can give rise to any of the previous forms or a combination thereof. It is to be further understood that the products of the processes described herein, can be isolated as enantiomerically and diastereomerically pure forms or as enantiomerically and diastereomerically enriched mixtures.

The sign "*" (asterisk) present in some formulae of the description and the claims indicates stereogenic (asymmetric) center, although the absence of asterisks does not necessarily imply that the compound lacks a stereocenter. Such formulae may refer to the racemate or to individual enantiomers or diastereomers, which may or may not be substantially pure.

A mixture of {R,S) enantiomers can contain the two single enantiomers in any ratio to each other. The enantiomeric purity is generally expressed as "enantiomeric excess" or ee and is defined, for example for the (S) enantiomer, as [(S-R)/(R+S)]x100, wherein S and R are respectively the amounts of the (S) and (R) enantiomers (as determined for example by GC or HPLC on a chiral stationary phase or polarimetry).

The term "racemic" refers to a sample of a chiral compound which contains both the (+) and (-) isomers in equal amount. The term "enantiomerically enriched" as used herein means that one of the stereoisomers of a compound is present in excess compared to the stereoisomers.

The term "enantiomerically pure" as used herein means that the enantiomeric purity is usually at least 96%, preferably at least 97%, more preferably at least 98%, even more preferably at least 99%, e.g. at least 99.5%. The term "diastereomerically enriched" as used herein means that a couple of enantiomers (i.e. stereoisomers related as mirror images) of a compound is present in excess compared to the other couple of enantiomers .

The term "diastereomerically pure" as used herein means that the diastereomeric purity is usually at least 96%, preferably at least 99%, more preferably at least 99.5%. The symbol (dashed bond) present in some of the formulae of the description and the claims indicates that the substituent is directed below the plane of the sheet.

The symbol — (wedge bond) present in some of the formulae of the description and the claims indicates that the substituent is directed above the plane of the sheet.

The term "enriched mixture" as used herein is intended means a diastereomerically enriched or a diastereomerically and enantiomerically enriched mixture of any of the compounds obtained by the process of the present invention. The compounds obtained by the chemical transformations of the present invention can be used for the following steps without further purification or can be separated and purified by employing conventional methods well known to those skilled in the art, such as recrystallization, column chromatography, or by transforming them into a salt or in a co-crystal with an appropriate co-former, or by washing with an organic solvent or with an aqueous solution, optionally adjusting pH.

It will be understood that any compound described herein may also describe any salts or co-crystals thereof.

The term "seed" refers to a crystalline substance that is added to a solution of the same substance to induce its crystallization. Seeding with a specific optical isomer often has the useful effect of promoting crystallization of the substance in the same form of the seed.

It should be noted that, during the conversion of the diastereomerically and enantiomerically pure cyclopropylmethanamine (3) or the salt thereof into the diastereomerically and enantiomerically pure propionamide of formula (4), neither epimerization (i.e. change of the relative ratio between diastereomers) nor racemization (conversion of the major enantiomer into the minor leading to a lower ee) are observed. Accordingly, the d.r. (diastereomeric ratio, namely the ratio of the percentage of one diastereoisomer in a mixture to that of the other diastereoisomer) and the ee detected in the pure cyclopropylmethanamine (3), or the salt thereof, are retained unchanged in the pure propionamide of formula (4).

According to its most general aspect, the present invention relates to a process for the preparation of a diastereomerically and enantiomerically pure propionamide of formula (4).

The first operation of the process of the invention, a), consists in the preparation of a diastereomerically and enantiomerically pure cyclopropylmethanamine (3) or a diastereomerically and enantiomerically pure salt of the cyclopropylmethanamine (3) with a chiral Bransted acid and includes, e.g., the following steps: c) preparing a diastereomerically enriched mixture or a diastereomerically and enantiomerically enriched mixture of a cyclopropylmethanamine (3): d) converting said enriched mixture of the cyclopropylmethanamine (3) into a diastereomerically and enantiomerically pure salt thereof by treatment with a chiral Bransted acid; and

e) optionally deblocking the diastereomerically and enantiomerically pure salt prepared in step d) to yield a diastereomerically and enantiomerically pure cyclopropylmethanamine (3).

The preparation of a diastereomerically enriched mixture or of a diastereomerically and enantiomerically enriched mixture of a cyclopropylmethanamine (3) according to step c) can be conveniently carried out according to a process including the following steps: c.i.1 ) converting 4-vynil-2,3-dihydrobenzofuran (5) into a diastereomerically enriched mixture or a diastereomerically and enantiomerically enriched mixture of a cyclopropanecarboxylate (6) in the presence of a catalyst:

wherein R1 is a C1 -C6 linear or branched alkyl, a C6-C10 aryl or a C1 -C6 linear or branched alkyl substituted with a C6-C10 aryl; c.i.2) converting said enriched mixture of a cyclopropanecarboxylate (6) into a diastereomerically enriched mixture or a diastereomerically and enantiomerically enriched mixture of a cyclopropanecarboxylic acid (7):

c.i.3) converting said enriched mixture of a cyclopropanecarboxylic acid (7) into a diastereomerically enriched mixture or a diastereomerically and enantiomerically enriched mixture of a cyclopropylmethanamine (3).

Step c.i.1 ) includes the conversion of 4-vynil-2,3-dihydrobenzofuran (5) into a diastereomerically and enantiomerically enriched mixture of a cyclopropanecarboxylate (6) or a diastereomerically enriched mixture thereof. This operation, in the case of the preparation of a diastereomerically and enantiomerically enriched mixture of a cyclopropanecarboxylate (6), is normally carried out in the presence of a chiral catalyst, preferably, according to the procedure described in international application WO 2015/123389 A1 which includes the treatment of 4-vynil-2,3-dihydrobenzofuran (5) with a diazoacetate (preferably ethyl diazoacetate) in the presence of a chiral catalyst derived from [Ru(p-cymene)Cl2]2 and {R,R)- (-)-/V,/V'-bis(3,5-di-fe/f-butylsalicylidene)-1 ,2-cyclohexanediamine. Alternatively, this operation can be carried out according to a Sharpless asymmetric dihydroxylation as described in the Organic Process Research & Development (2003), 7, 821 -827, followed by a cyclopropanation according to Wadsworth and Emmons as described in the Organic Process Research & Development (2002), 6, 618-620.

In the case of the preparation of a diastereomerically enriched mixture of a cyclopropanecarboxylate (6), operation c.i.1 ) is carried out in the presence of a catalyst, preferably, according to the procedure described in international application WO 01/27107 A1 which includes, as key steps, the conversion of 4-vynil-2,3-dihydrobenzofuran (5) into (E)-3- (2,3-dihydrobenzofuran-4-yl)acrylate and the following palladium-catalysed cyclopropanation.

All these procedures are incorporated herein by reference.

The enriched mixture of cyclopropanecarboxylate (6) thus obtained, optionally isolated, is further converted by hydrolysis into a diastereomerically and enantiomerically enriched mixture of cyclopropanecarboxylic acid (7), or into a diastereomerically enriched mixture thereof, according to step c.i.2).

This step can be performed using one of the methods known to the person skilled in the art, for example one of those described in Theodora W. Green, Protective Groups in Organic Synthesis, John Wiley & Sons (1999), pages 373-428, which are herein incorporated by reference.

Preferably, said hydrolysis is carried out by contacting the enriched mixture of cyclopropanecarboxylate (6) with a hydroxide or a carbonate of an alkali metal (such as KOH, NaOH, LiOH, K2CO3, Na2CC>3, L12CO3, CS2CO3) in a water miscible solvent (e.g. methanol, ethanol, tetrahydrofuran, dimethoxyethane, dioxane or a mixture thereof) or a mixture thereof with water. The amount of the hydroxide or carbonate of the alkali metal used is normally from 1 to 10 equivalents, preferably from 2 to 8 equivalents, more preferably from 2.5 to 6 equivalents, compared to the molar quantity of the cyclopropanecarboxylate (6).

The resulting enriched mixture of the cyclopropanecarboxylic acid (7), optionally isolated, is further converted into the desired diastereomerically and enantiomerically enriched cyclopropylmethanamine (3), or into a diastereomerically enriched mixture thereof, according to step c.i.3). Preferably this operation is carried out according to the following steps: c.i.3.a) converting said enriched mixture of cyclopropanecarboxylic acid (7) into a diastereomerically enriched mixture or a diastereomerically and enantiomerically enriched mixture of a cyclopropane amide (8):

c.i.3.b) reducing said enriched mixture of cyclopropane amide (8):

Step c.i.3.a) can be carried out according to any one of the procedures generally known in the art to convert a carboxylic acid into the corresponding amide, e.g., via the formation of an acyl halide (preferably an acyl chloride) and the subsequent treatment with ammonia.

According to a preferred operative condition, the conversion of the enriched mixture of cyclopropanecarboxylic acid (7) into the corresponding cyclopropane amide (8) according to step c.i.3.a) is performed by treating the enriched mixture of cyclopropanecarboxylic acid (7) with carbonyldiimidazole (CDI) to yield the corresponding imidazolide, followed by the addition of ammonia or, preferably, by quenching in an aqueous solution of ammonium hydroxide (e.g. a 24%, a 28% or a 30% (w/w) aqueous solution thereof). This reaction is normally carried out in an inert solvent, such as, for example, acetonitrile, dimethylacetamide, or preferably THF and maintaining the temperature from -10 to 25 °C, preferably from 0 to 10 °C, during both the carboxylic acid activation phase and in the reaction phase envisaging condensation with ammonia.

The reduction of the enriched mixture of cyclopropane amide (8) into the enriched mixture of cyclopropylmethanamine (3) according to step c.i.3.b) can be accomplished according to anyone of the methods generally known in the field, preferably at temperatures between 0 and 30 °C. Examples of reducing agents suitable for the aim are boron derivatives selected the group comprising, more preferably consisting of, borohydrides of alkali metals (preferably lithium borohydride and potassium borohydride) or boranes (e.g. diborane); alternatively boranes can be used in the form of a complex, for example with tetrahydrofuran, diethel ether or dimethyl sulfide. Preferably, the reducing agent is an aluminium derivative selected from the group comprising, more preferably consisting of, aluminium hydride, lithium aluminium hydride, di-/so-butyl aluminium hydride (Dibal-H), sodium bis(2- methoxyethoxy)aluminum hydride (commercially available as toluene solution as Red-AI ^® , a registered trademark of Sigma-Aldrich Co. LLC) and lithium tri-ie f-butoxyaluminium hydride. The amount of reducing agent is generally comprised from 1 to 10 equivalents, preferably from 2 to 5 equivalents, more preferably from 3 to 4 equivalents, with respect to the amount of cyclopropane amide (8).

The reduction of the enriched mixture of cyclopropane amide (8) can be carried out in an organic solvent, such as for example an ether (preferably tetrahydrofuran, dioxane, di-/so- propyl ether, diethyl ether, 2-methyl tetrahydrofuran, cyclopentylmethyl ether or methyl tert- butyl ether), a halogenated solvent (preferably dichloromethane), or a hydrocarbon, aliphatic or aromatic (preferably hexane or toluene).

The optionally isolated enriched mixture of cyclopropylmethanamine (3) prepared according to step c), e.g. according to the procedures detailed above under steps c.i.1 ) to c.i.3), is subsequently treated, in step d), with a chiral Bransted acid selected from the group comprising, preferably consisting of, (1 R)-{- )-10-camphorsulfonic acid, (1 S)-(+)-10- camphorsulfonic acid, /V-formyl-L-leucine, L-(-)-malic acid, D-(+)-malic acid, (R)-(-)-mandelic acid, (S)-(+)-mandelic acid, D-(-)-tartaric acid and L-(+)-tartaric acid, to obtain the corresponding salt, which is eventually purified by diastereomeric salt resolution.

Preferably step d) entails the treatment of the enriched mixture of cyclopropylmethanamine (3) with a chiral Br0nsted acid selected from the group comprising, more preferably consisting of, (R)-(-)-mandelic acid, (S)-(+)-mandelic acid, D-(-)-tartaric acid and L-(+)-tartaric acid. The diastereomeric salt resolution is generally performed by heating to a temperature next to the boiling point of the used solvent, followed by cooling to a temperature from 0 to 30 °C. The formation of the salt is complete within some minutes but the reaction time can be extended to several hours without causing any disturbance. The molar ratio of the chiral Bransted acid with respect to the enriched mixture of cyclopropylmethanamine (3) is normally from 0.5 to 1. Examples of solvents suitable for the formation and fractionation of the salts are water miscible solvents, such as alcohols (e.g. methanol, ethanol or 2-propanol) or acetates (preferably ethyl acetate or /so-propylacetate) optionally in mixture with water.

The volume of the solvent is normally from 15 mL to 50 ml_, preferably from 20 ml_ to 45 ml_, more preferably from 25 mL to 42 ml_, per gram of the enriched mixture of cyclopropylmethanamine (3); even more preferably, said volume is 38 mL per gram of said enriched mixture.

The ratio between the water miscible solvent and water in said mixtures can vary in a very wide range; preferably from 1 :1 to 10:1 (V/V), more preferably from 2:1 to 8:1 (V/V), even more preferably from 3:1 to 5:1 (V/V).

In a possible variant of this operation, a seed of the desired optically active isomer is added to the solution of the salt before cooling it down.

Optional step e) comprises deblocking the diastereomerically and enantiomerically pure salt prepared in step d) to yield a diastereomerically and enantiomerically pure cyclopropylmethanamine (3). Preferably, said deblocking is carried out by contacting the pure salt prepared in step d) with a hydroxide or a carbonate of an alkali metal (such as KOH, NaOH, LiOH, K2CO3, Na2CC>3, L12CO3, CS2CO3) in a mixture comprising a water miscible solvent (e.g. methanol, ethanol, tetrahydrofuran, dioxane and mixtures thereof) or a halogenated solvent (preferably dichloromethane) and water. The amount of the hydroxide or carbonate of the alkali metal used is normally from 1 to 5 equivalents, preferably from 2 to 4 equivalents, compared to the molar quantity of diastereomerically and enantiomerically pure salt used.

The volume of the solvent is normally from 5 mL to 50 ml_, preferably from 7 mL 20 ml_, more preferably from 10 mL 5 mL per gram of the pure of cyclopropylmethanamine (3). The diastereomerically and enantiomerically pure cyclopropylmethanamine (3) or the diastereomerically and enantiomerically pure salt of the cyclopropylmethanamine (3) prepared according to step a), preferably according to the operations detailed under steps c) to e), are thus converted into a diastereomerically and enantiomerically pure propionamide of formula (4) by treatment with 1 -(1 /-/-imidazol-1 -yl)propan-1-one (2), according to operation b). 1 -(1 /-/-imidazol-1 -yl)propan-1 -one (2) used as reagent in this operation is commercially available; alternatively, it can be prepared according to standard techniques in organic synthesis, for example, by treating propionic acid with CDI, e.g., according to the conditions detailed above to carry out the carboxylic acid activation phase of step c.i.3.a).

The coupling between the pure cyclopropylmethanamine (3) or the pure salt thereof and 1 -(1 /-/-imidazol-1 -yl)propan-1 -one (2) is normally carried out at a temperature from -20 to 40 °C, preferably from 0 to 30 °C, for example from 5 to 25 °C, in at least one organic solvent, preferably an aprotic polar solvent, such as an ether (preferably tetrahydrofuran, 2- methyltetrahydrofuran, methyl-ie f-butyl ether or cyclopentylmethyl ether), an acetate (preferably ethyl acetate or /so-propylacetate), a chlorinated solvent (such as dichloromethane), Λ/,/V-dimethylacetamide, Λ/,/V-dimethylformamide, /V-methylpyrrolidone, acetonitrile or a mixture thereof. More preferably said coupling step is carried out in an organic solvent or in a mixture of organic solvents which are soluble in each other. Even more preferably this step is carried out in a homogenous mixture (e.g. a solution). The amount of 1 -(1 /-/-imidazol-1 -yl)propan-1 -one (2) is conveniently from 1 to 2 equivalents, preferably from 1 .1 to 1 .8 equivalents, more preferably from 1 .3 to 1 .6 equivalents, with respect to the molar quantity of the diastereomerically and enantiomerically pure cyclopropylmethanamine (3) or the pure salt thereof.

The process object of the most general aspect of the invention may additionally comprise a further step f) including the crystallization of the diastereomerically and enantiomerically pure propionamide of formula (4).

Said crystallization is generally performed by heating a solution of the pure propionamide of formula (4) to a temperature next to the boiling point of the used solvent, followed by cooling to a temperature between 0 and 30 °C. Examples of solvents suitable for the aim are water miscible solvents, such as alcohols (e.g. methanol, ethanol) optionally in mixture with water; aliphatic or aromatic hydrocarbons (preferably hexane, cyclohexane or toluene); an acetate (preferably ethyl acetate or /so-propylacetate); or mixtures thereof.

Preferably the diastereomerically and enantiomerically enriched mixture of the cyclopropylmethanamine (3) prepared in operation c) of the process, is an enantiomerically enriched irans-cyclopropylmethanamine (3A):

irans-enantiomerically enriched mixture

In this case, the diastereomerically and enantiomerically pure cyclopropylmethanamine (3) prepared in operation a) is a diastereomerically and enantiomerically pure irans- cyclopropylmethanamine (3B) and the process of the invention leads to the formation of a diastereomerically and enantiomerically pure propionamide of formula (4A):

The diastereomerically and enantiomerically pure salts between cyclopropylmethanamine (3) and a chiral Bransted acid selected from the group consisting of (R)-(-)-mandelic acid, (S)-(+)-mandelic acid, /V-formyl-L-leucine, L-(-)-malic acid, D-(+)-malic acid, D-(-)-tartaric acid or L-(+)-tartaric acid are novel intermediates and they are a further object of the present invention. A further object of the present invention relates to the use of such intermediates for preparing the diastereomerically and enantiomerically pure propionamide of formula (4), preferably the diastereomerically and enantiomerically pure propionamide of formula (4A).

The diastereomerically and enantiomerically pure propionamide of formula (4) obtained by the processes object of the present invention can be converted into a co-crystal thereof in a further optional step.

When the pure propionamide of formula (4), or any other of the compounds described in the present application, are obtained with a degree of chemical purity not suitable for the inclusion in a medicament, the processes object of the present invention entail a further step of purification, for example by means of chromatography or crystallization, optionally after formation of an addition compound, such as for example a salt or a co-crystal, or by washing with an organic solvent or an aqueous solution, optionally adjusting the pH.

The invention will be further illustrated by the following examples.

In the examples, the enantiomeric ratio of irans-(2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine was determined after conversion of an aliquot of the sample into Tasimelteon, by means of a Chiral HPLC (95:5 nhexane/2-propanol at 25 °C, Chiralpak AD-H from Daicel, 250 mm x 4.6 mm, 5 μηη, at 230 nm): 26.0 min (S,S isomer), 28.1 min (R,R isomer, i.e. Tasimelteon).

The chemical purity of Tasimelteon was determined by means of the following chromatographic method:

Column: YMC-Pack ODS-AM 150 x 4.6 mm, 3 μηι

Mobile Phase A: 10 mM KH ₂ P0 ₄ in water pH = 3 (H ₃ P0 ₄ )

Mobile Phase B: Acetonitrile

Diluent: 1 :1 (V/V) Mixture of water and acetonitrile

Flow Rate: 1.0 mL/min

Runtime: 40 min

Column Temperature 30 °C

Autosampler Temperature: Ambient

Injection Volume: 5 μΙ_

Detection: 210 nm

Gradient Program: Time (min.) A (%) B (%)

0 85 15

15 45 55

20 20 80

25 20 80

30 85 15

40 85 15

Example 1

Preparation of ((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamin ium (D)- (-)-tartrate.

(R,R):(S:S)=92:8

To a dispersion of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine having an enantiomeric ratio (R,R):(S,S) of 43:57 (5.00 g, 26.4 mmol) in a 3.5: 1 (v/v) mixture of methanol and water (225 mL), (D)-(-)-tartaric acid (3.96 g, 26.4 mmol) was added. The resulting suspension was heated to reflux (about 70 °C) until a clear solution was obtained, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The obtained solid was filtered, washed with a 3.5: 1 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 3.97 g of the (D)-(-)- tartrate salt (44% yield over irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine ) having an enantiomeric ratio (R,R):(S,S) of 76:24 were obtained. The so obtained (D)-(-)-tartrate salt was dissolved under stirring in a 4.5: 1 (v/v) mixture of methanol and water (80 mL) at 70 °C, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with a 4.5: 1 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 2.32 g of the (D)-(-)-tartrate salt (60% yield over irans-(2-(2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine (D)-(-)-tartrate salt) having an enantiomeric ratio {R,R):{S,S) of 92:8 were obtained.

Example 2

Preparation of ((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamin ium (1 R)-(- )-10-camphorsulfonate.

(R,R):(S:S)=32:68

To a dispersion of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine having an enantiomeric ratio (R,R):(S,S) of 58:42 (5.00 g, 26.4 mmol) in methanol (50 ml_), ((1 /?)-(-)-10-camphorsulfonic acid (6.14 g, 26.4 mmol) was added. The resulting suspension was heated to reflux (about 70 °C) until a clear solution was obtained, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The obtained solid was filtered, washed with methanol previously cooled to 0 °C and dried under reduced pressure at 45 °C. 6.01 g of the (1 R)-(-)-10-camphorsulfonate salt (54% yield over frans-(2-(2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine) having an enantiomeric ratio (R,R):(S,S) of 48:52 were obtained.

The so obtained (1 R)-(- )-10-camphorsulfonate salt was dissolved under stirring in methanol (30 mL) at 65 °C, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with methanol previously cooled to 0 °C and dried under reduced pressure at 45 °C. 3.50 g of the (1 R)-(-)-10- camphorsulfonate salt (60% yield over irans-(2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine (1 R)-(- )-10-camphorsulfonate salt) having an enantiomeric ratio {R,R):{S,S) of 32:68 were obtained.

Example 3

Preparation of ((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamin ium (R)- (-)-mandelate. This example is representative of step d) of the process of the invention.

(R,R):(S:S)=98:2

To a dispersion of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine having an enantiomeric ratio (R,R):(S,S) of 43:57 (5.00 g, 26.4 mmol) in methanol (42 ml_), (/?)-(- )-mandelic acid (4.02 g, 26.4 mmol) was added. The resulting suspension was heated to reflux (about 70 °C) until a clear solution was obtained, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The obtained solid was filtered, washed with methanol previously cooled to 0 °C and dried under reduced pressure at 45 °C. 3.78 g of the (R)-(-)-mandelate salt (42% yield over irans-(2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine) having an enantiomeric ratio (R,R):(S,S) of 86:14 were obtained.

The so obtained (/?)-(- )-mandelate salt was dissolved under stirring in a 9: 1 (v/v) mixture of methanol and water (22 mL) at 70 °C, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with a 9:1 (v/v) methanol/water mixture previously cooled to 0 °C and dried under reduced pressure at 45 °C. 2.60 g of the (R)-(-)-mandelate salt (73% yield over irans-(2-(2,3-dihydrobenzofuran- 4-yl)cyclopropyl)methanamine (/?)-(- )-mandelate salt) having an enantiomeric ratio (R,R):(S,S) of 98:2 were obtained.

Example 4

Preparation of ((1 R,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamini um (-)-0,0'-dibenzoyl-L-tartrate.

(R,R):(S:S)=59:41

To a dispersion of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine having an enantiomeric ratio (R,R):(S,S) of 58:42 (5.00 g, 26.4 mmol) in a 30:70 (v/v) mixture of methanol and water (218 ml_), (-)-0,0'-dibenzoyl-L-tartaric acid (9.94 g, 26.4 mmol) and water (150 mL) were added. The resulting suspension was heated to reflux (about 70 °C) and maintained under stirring for 2 hours, then it was cooled to 25 °C over 2 hours. The obtained solid was filtered, washed with a 30:70 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 13.49 g of the (-)-0,0'-dibenzoyl-L-tartrate salt (90% yield over irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine ) having an enantiomeric ratio (R,R):(S,S) of 58:42 were obtained.

Water (100 mL) was added to the so obtained (-)-0,0'-dibenzoyl-L-tartrate salt dispersed under stirring in a 1 : 1 .5 (v/v) mixture of methanol and water (175 mL) at 70 °C. The mixture was cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with a 1 : 1 .5 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 1 1 .46 g of the (-)-0,0'-dibenzoyl-L-tartrate salt (86% yield over frans-(2-(2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine Ο,Ο'-dibenzoyl-L-tartrate salt) having an enantiomeric ratio (R,R):(S,S) of 59:41 were obtained.

Example 5

Preparation of ((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamin ium L-(- )-Malate.

(R,R):(S:S)=50:50

To a dispersion of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine having an enantiomeric ratio (R,R):(S,S) of 58:42 (5.00 g, 26.4 mmol) in a 8: 1 (v/v) mixture of methanol and water (45 ml_), L-(-)-malic acid (3.54 g, 26.4 mmol) was added. The resulting suspension was heated to reflux (about 70 °C) until a clear solution was obtained, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The obtained solid was filtered, washed with a 8: 1 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 6.42 g of the L-(-)-malate salt (76% yield over irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine ) having an enantiomeric ratio (R,R):(S,S) of 51 :49 were obtained.

The so obtained L-(-)-malate salt was dissolved under stirring in a 6:1 (v/v) mixture of methanol and water (35 mL) at 70 °C, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with a 6:1 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 5.47 g of the L-(-)-malate salt (88% yield over trans-{2-{2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine L-(-)-malate salt) having an enantiomeric ratio {R,R):{S,S) of 50:50 were obtained.

Example 6

Preparation of ((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamin ium N- formyl-L-leucine salt.

To a dispersion of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine having an enantiomeric ratio {R,R):{S,S) of 43:57 (5.00 g, 26.4 mmol) in / ^' so-propylacetate (42 mL), /V-formyl-L-leucine (4.20 g, 26.4 mmol) was added. The resulting suspension was heated to reflux (about 70 °C) until a clear solution was obtained, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with methanol previously cooled to 0 °C and dried under reduced pressure at 45 °C. 5.44 g of the /V-formyl-L-leucine salt (74% yield over irans-(2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine) having an enantiomeric ratio (R,R):(S,S) of 60:40 were obtained.

Example 7

Preparation of irans-4-(oxiran-2-yl)-2,3-dihydrobenzofuran. This example is representative of step c.i.1 ) of the process of the invention.

(S):(R)=95:5 (S):(R)=95:5

Chlorotrimethylsilane (10.55 g, 97.1 mmol) was added to a solution cooled to 0-5 °C of frans-1 -(2, 3-dihydrobenzofuran-4-yl)ethane-1 ,2-diol having an enantiomeric ratio {S):(R) of 95:5 (10.00 g, 55.5 mmol) (prepared according to the procedure described Organic Process Research & Development (2003), 7, 821 -827) and trimethyl orthoacetate (1 1 .74 g, 97.7 mmol) in tetrahydrofuran (50 mL).

The mixture was maintained under stirring at the same temperature until complete conversion into 2-chloro-2-(2,3-dihydrobenzofuran-4-yl)ethyl acetate was achieved (about 2 hours), then a solution of potassium ie f-butoxide (8.72 g, 77.7 mmol) in tetrahydrofuran (45 mL) was added thereto monitoring that internal temperature did not exceed 0 °C.

The mixture was maintained under the same conditions until complete conversion into (S)-4-(oxiran-2-yl)-2,3-dihydrobenzofuran (about 1 hour), then water (90 mL) and hydrochloric acid 2% (about 7 mL) were added up to obtaining a pH ~ 7.0.

The resulting phases were separated and the organic layer washed with brine. The collected aqueous phases were extracted with methyl ie f-butyl ether, then the organic phases were combined and evaporated under reduced pressure to a residue, which was co-evaporated with 1 ,2-dimethoxyethane, diluted with the latter solvent (18 mL) and used as such in the following example 8. Example 8

Preparation of irans-2-(2,3-dihydrobenzofuran-4-yl)cyclopropane-1 -carboxylic acid. This example is representative of steps c.i.1 ) and c.i.2) of the process of the invention.

To a solution of sodium ie f-butoxide (10.67 g, 1 1 1 mmol) in 1 ,2-dimethoxyethane (27 mL) maintained at 20-25 °C, triethyl phosphonoacetate (28.62 g, 128 mmol) was added dropwise. The resulting mixture was maintained under stirring at 20-25 °C until a clear solution was achieved, then the 1 ,2-dimethoxyethane solution prepared in example 7 (55.5 mmol theoretical) was added dropwise monitoring that the internal temperature did not exceed 25 °C.

The mixture was evaporated under reduced pressure at 50 °C in order to halve the initial volume, then the resulting mixture was heated to 75 °C and maintained under stirring at the same temperature up to the obtainment of complete conversion into ethyl trans-2-(2,3- dihydrobenzofuran-4-yl)cyclopropane-1 -carboxylate (about 20 hours). To the mass cooled to 20-25 °C, water (45 mL) and a 50% (w/w) solution of sodium hydroxide in water (26.64 g, 333 mmol) were added. The mixture was heated again to 55-60 °C up to obtaining complete conversion into irans-2-(2,3-dihydrobenzofuran-4- yl)cyclopropane-1 -carboxylic acid (about 1 hour).

The reaction mixture was concentrated under reduced pressure in order to remove 1 ,2- dimethoxyethane, then the resulting aqueous phase was washed with toluene. The pH of the aqueous layer was adjusted to a value ~ 1 .0 by adding a 20% (w/w) hydrochloric acid (about 60 mL), then toluene (45 mL) was added.

The resulting phases were separated and the aqueous phase was extracted with toluene. The collected organic phases were washed with water and concentrated to residue under reduced pressure. The resulting oil was used without further purification in the following example 9. Example 9

Preparation of irans-2-(2,3-dihydrobenzofuran-4-yl)cyclopropane-1 -carboxamide. This example is representative of step c.i.3.a) of the process of the invention.

To a solution cooled to 0-5 °C of the acid prepared as described in example 8 (55.5 mmol theoretical) in tetrahydrofuran (56 ml_), 1 ,1 '-carbonyldiimidazole (10.80 g, 6.6 mmol) was added portionwise.

The mixture was heated to 20-25 °C and maintained under stirring at the same temperature until complete conversion into imidazolide derivative (about 2 hours), then it was poured into a 28-30% aqueous ammonia solution (56 mL) previously cooled to 0-5 °C. At the end of the addition the mixture was heated to 20-25 °C and maintained under stirring until complete conversion into irans-2-(2,3-dihydrobenzofuran-4-yl)cyclopropane-1 -carboxamide was achieved (about 1 hour), then it was concentrated under reduced pressure in order to halve the initial volume. The resulting solid was filtered, washed with water and dried under vacuum at 45 °C to yield 7.80 g of irans-2-(2,3-dihydrobenzofuran-4-yl)cyclopropane-1 - carboxamide (69% yield from frans-1 -(2, 3-dihydrobenzofuran-4-yl)ethane-1 ,2-diol).

Example 10

Preparation of irans-(2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamin example is representative of step c.i.3.b) of the process of the invention.

To a suspension of lithium aluminium hydride (5.10 g, 134 mmol) in tetrahydrofuran (80 mL), the irans-2-(2,3-dihydrobenzofuran-4-yl)cyclopropane-1 -carboxamide (7.80 g, 38.4 mmol) prepared as described in example 9 was added portionwise. The resulting mixture was maintained under stirring at 65 °C until complete conversion into the desired product (about 5 hours), then it was cooled to -5 °C. Water (5.1 ml_), a 15% (w/w) solution of sodium hydroxide in water (5.1 mL) and water (15.3 mL) were subsequently added to the reaction mixture, monitoring that internal temperature did not exceed 30 °C. The precipitated solid was filtered and slurried in tetrahydrofuran. The resulting organic phases were combined and concentrated under reduced pressure to a residue which was eventually co-evaporated with methanol up to a residual oil having an enantiomeric ratio (R,R):(S,S) of 95:5.

Example 11

Preparation of ((1 R,2R)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanaminiu m (D)- (-)-tartrate. This example is representative of step d) of the process of the invention.

(R,R):(S:S)=95:5 (R,R):(S:S) > 99.9:0.1

To a methanol solution (225 mL) heated to 50 °C of the amide (38.4 mmol theoretical) prepared as described in example 10, a solution of D-(-)-tartaric acid (5.76 g, 38.4 mmol) in methanol (25 mL) was added

After heating the mixture to 70 °C, water was added thereto until a clear solution was obtained (about 50 mL).

The mass was cooled to to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 4 hours, then it was filtered and the panel washed with a 4:1 (v/v) mixture of methanol and water previously cooled to 0 °C. The resulting solid (10.90 g) was dried under vacuum at 45 °C (84% yield with respect to irans-(2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine) showing an enantiomeric ratio (R,R):(S,S) of 99: 1 .

The so obtained (D)-(-)-tartrate salt was dissolved under stirring in a mixture of methanol (190 mL) and water (45 mL) at 70 °C, then it was cooled to 45 °C, heated again to 60 °C and eventually cooled to 25 °C over 2 hours. The resulting solid was filtered, washed with a 4:1 (v/v) mixture of methanol and water previously cooled to 0 °C and dried under reduced pressure at 45 °C. 9.80 g of the (D)-(-)-tartrate salt (90% yield over trans-{2-{2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine (D)-(-)-tartrate salt) having an enantiomeric ratio {R,R):{S,S) > 99.9:0.1 were obtained.

Example 12

Preparation of ((1 R,2R)-2-(2,3-dihydrobenzofuran-4-yl)cyclopropyl)methanamine. This example is representative of optional step e) of the process of the invention.

(R,R):(S:S > 99.9:0.1 {R,R):{S:S) > 99.9:0.1

To a suspension in dichloromethane (50 mL) and water (50 mL) of the (D)-(-)-tartrate salt (9.80 g, 28.9 mmol) prepared as described in example 1 1 , a 30% (w/w) solution of sodium hydroxide was added up to obtaining a pH > 9. At the end of the addition, the phases were separated and the aqueous layer was extracted with dichloromethane. The collected organic phases were evaporated under reduced pressure to a residue which was dissolved in tetrahydrofuran (8 mL) and used as such in the following example 13.

Example 13 Preparation of Tasimelteon. This example is representative of step b) of the process of the invention.

To a solution cooled to 0 °C of propionic acid (3.2 g, 43.2 mmol) in tetrahydrofuran (50 mL), 1 ,1 '-carbonyldiimidazole (7.0 g, 43.2 mmol) was added portionwise. The mixture was maintained under stirring at the same temperature until complete conversion into 1 -propionyl imidazolide (about 1 hour), then the solution of ((1 /?,2/?)-2-(2,3-dihydrobenzofuran-4- yl)cyclopropyl)methanamine in tetrahydrofuran prepared according to example 12 was added monitoring that the internal temperature did not exceed 5 °C.

The mass was warmed to 25 °C and maintained under stirring at the same temperature until complete conversion into Tasimelteon (about 2 hours), then it was concentrated under reduced pressure.

After having dissolved the residue in a 1 :1 (v/v) mixture of toluene and water (50 mL), the pH of the mixture was adjusted to values > 9 by adding a 15% (w/w) solution of sodium hydroxide in water (about 5 mL). The phases were separated and the aqueous layer was counter-extracted with toluene. Water (20 ml.) and 5% (w/w) hydrochloric acid (about 5 mL) were added to the collected organic phases up to obtaining a pH < 3. The phases were separated and the aqueous layer was counter-extracted with toluene. The collected organic phases were washed with water and concentrated under reduced pressure at 45 °C up to an oil residue which was co-evaporated with / ^' so-propylacetate and eventually crystallized from a 1 : 1 (v/v) mixture of /so-propylacetate and cyclohexane (30 mL). 6.00 g of Tasimelteon (85% yield over trans-(2-(2,3- dihydrobenzofuran-4-yl)cyclopropyl)methanamine (D)-(-)-tartrate salt) having an enantiomeric ratio {R,R):{S,S) > 99.9:0.1 and a chemical purity, as determined by HPLC analysis, of 99.8% were obtained.