PROCESS FOR PREPARATION OF SUBSTITUTED PROPENOIC ACID ESTERS FIELD OF THE INVENTION The present invention relates to a novel process for the preparation of substituted propenoic acid esters using active methylene compounds and N, N dimethyl formamide-dimethyl sulfate complex.

BACKGROUND OF THE INVENTION Substituted propenoic acid esters, especially amino-substituted derivatives like (3-amino acrylic acid esters are significantly important in the synthesis of quinolones (JP 02215749 A2,1990; Leibigs Ann. Chem. 29-37, 1987).

Nalidixic acid was the first quinolone introduced to clinical practice, and is still in use for treatment of urinary tract infections caused by gram- negative pathogens.

Since the introduction of Nalidixic acid in the early 1960s, substantial improvements have been made in the antibacterial spectrum and potency of quinolones. Additionally, newer quinolones are well absorbed and distributed throughout the body making them useful for the treatment of a variety of systemic infections including those of the respiratory tract, gastrointestinal tract, the ear, nose, and throat, sexually transmitted diseases and bone infections (Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Edition, 1991, Vol. 2,855).

Along with the increase in the importance of quinolones as an antibacterial agent, the synthesis of quinolones and the intermediates like ß- amino acrylic acid esters used for their synthesis also gained importance.

The present invention discloses a safe, economical and facile route for the preparation of substituted propenoic acid esters.

DESCRIPTION OF THE PRIOR ART There are various methods for the preparation of the useful-amino acrylic acid esters.

U S Patent No. 4,772,711 (Englaender et al, 1988) discloses a method for the preparation of 3 amino acrylic acid esters by reacting an alkali salt of a beta hydroxy acrylic acid ester with an amine salt.

U S Patent No. 5,030,747 (Blank et al 1991) discloses a method of preparation of beta amino acrylic acid esters by reaction of beta hydroxy acrylic acid ester alkali metal salts with ammonium salts in an aprotic organic solvent, or in an aprotic organic solvent in mixture with a protic organic solvent miscible with the aprotic solvent, to give high 90% yield of the reaction product compared to 75% yield of the Englaender method (U S Patent No.4,772,711).

The starting alkali salt of beta hydroxy acrylic acid ester for both the above methods of US Patent Nos. 4,772,711 and 5,030,747 is obtained from carbon monoxide, alcoholate and acetic acid esters in a pressure reaction requiring 20 to 50 bar. Thus, both these methods requires high pressure

apparatus. Moreover, the high toxicity and flammability of carbon monoxide demands special safety devices.

Lang & Cohen (Journal of Medicinal Chemistry, Vol. 18 No. 4,441-443) describes a method for the production of ethyl-3-dimethyl amino acrylate by the reaction of ethyl propiolate with aqueous dimethyl amine in 47% yield.

However, the process warrants use of costly ethyl propiolate as one of the starting materials.

In the process described in Tetrahedron letters, 4061,1976 and Liebigs Annalen Der Chemie Vol. 1980, No. 7,991, highly toxic iron pentacarbonyl is used in the reaction of methyl aciylate with t-butoxy bis (dimethylamino) methane. Moreover, there is polymerization of acrylic acid ester, which makes the reaction product more difficult to isolate, and is a disadvantage of the process.

P-Dimethyl amino acrylic acid ester is also obtained by the reaction of t-butoxy bis (dimethylamino) methane with ethyl acetate at 170°C (Chemische Berichte 2709,104,1971). The process has to be carried out in a sealed tube and high pressures are attained at the end of a volatile reaction. It is also known, that when methoxy bis (dimethylamino) methane is reacted with ethyl butyrate, no reaction product is obtained at all (Organic Preparation Proceedings, International 67,10,1978).

US Patent No. 5,446,192 (Kraus et al, 1995) discloses a method for production of P-amino acrylic acid esters by reacting acetic acid esters with amino acid esters at 0.5 to 10 bar (preferably 1 to 5 bar) and 50-70°C

(preferably 80°C to 150°C) in an aprotic polar solvent. Apart from the high temperature and pressure required by the process, the amino acid esters are costly.

The above described methods are both cumbersome and costly. Hence there arose a need to develop a facile, novel scheme to prepare substituted propenoic acid esters.

SUMMARY OF THE INVENTION The object of the invention is to provide for a safe, economical, facile route for the preparation of substituted propenoic acid esters.

The present invention provides a process for the preparation of substituted propenoic acid esters of general formula I. wherein R is C1-C4 alkyl group, said process comprises, reacting an active methylene compound of the general formula II, wherein Rl is Na+ or K+ and R2 is Cl-C4 alkyl group, with, N, N-dimethyl amino methoxymethylium methyl sulfate of formula III:

in the presence of a solvent.

DETAILED DESCRIPTION OF THE INVENTION The synthetic utility, of (3-amino acrylic acid esters is ever increasing, as mentioned earlier, in the examples of quinolones, which are marketed worldwide. To make such products more economical, it is necessary to find a commercially viable and safe route. In literature, there are various methods of reported for the synthesis of R-amino acrylic acid esters as described above.

However, the risks involved in the processes are high due to high temperatures and/or pressures involved, hazards of reactant and product costs, all of which demand for a new route.

The present invention relates to a cost effective and safe process. The present invention provides a process for the preparation of substituted propenoic acid esters of formula (I) : wherein R is Cl-C4 alkyl group, by reacting active methylene compounds of general formula (II):

wherein R, is Na+ or K+ and R2 is C-C4 alkyl group, with, N, N- dimethyl formamide-dimethylsulfate complex of general formula (III): The R2 group of the active methylene compound of general formula (II) used in the present invention is preferably methyl or ethyl.

The active methylene compound is preferably cooled before the reaction, to a temperature range of 5-20°C and preferably to around 10°C. The reaction between compounds II and III is carried out in an inert atmosphere, preferably nitrogen atmosphere.

N, N-dimethylformamide-dimethylsulfate complex i. e.

N, N-dimethylamino methoxymethylium methyl sulfate (III) was prepared according to literature procedure (Organic Synthesis, Collective Vol. V).

The reaction according to the process of the invention may be represented by the following scheme: CH3 o CH3 3 0 COOL C/Xo° C H 3 0-S---O C H 3+<HO H, C S0R2 H Oliventchu" soy CH3 ! CH3

Ethylene dichloride is preferably used as solvent, but benzene, toluene or chloroform can also be used.

According to the reaction scheme, methyl alkali malonate, such as methyl potassium malonate (II) was treated with N, N-dimethylamino methoxymethylium methyl sulfate (III) to give 2-propenoic acid, 3- (dimethylamino), methyl ester, (E) in 68% yield.

EXAMPLES EXAMPLE 1: Preparation of methyl potassium malonate by using dimethyl malonate.

A 20 lit. round bottom flask was charged with 3 lit. of methanol under nitrogen. To it was added 2 Kg. of dimethylmalonate and it was cooled to 0- 20°C, preferably to 10°C. To this cooled solution, methanolic potassium hydroxide solution (prepared by the slow addition of 960 gm. of potassium hydroxide in 3 lit. of methanol under nitrogen) was added. The reaction mixture was stirred for 5-10 hr., preferably 7 hr. The reaction mixture was then cooled to 0-10°C, preferably 5°C for 30 mm. The solid which separated out was filtered to give 1.98 Kg. of methyl potassium malonate.

EXAMPLE 2: Preparation of methyl potassium malonate by using diethyl malonate.

A 1 lit. round bottom flask was charged with 150ml. of methanol under nitrogen. To it was added 100 gm. of diethyl malonate and it was cooled to 0- 15°C, preferably to 10°C. To this cooled solution, methanolic potassium hydroxide solution (prepared by the slow addition of 40 gm. of potassium hydroxide in 150 ml. of methanol under nitrogen) was added. The reaction mixture was stirred for 7 hr. The reaction mixture was then cooled to 5°C for 30 mm. The solid which separated out was filtered to give 85 gm. of methyl malonate.

Similarly, methyl sodium malonate was also prepared, using the above procedures.

EXAMPLE 3: Preparation of 2-propenoic acid, 3- (dimethylamino), methyl ester, (E).

In a 20 lit. round bottom flask, 1.98 kg. of methyl potassium malonate in 8 lit. of ethylene dichloride was added. The reaction mixture was cooled to 5-20°C, preferably to 10°C, and 3.2 Kg. of N, N-dimethylamino methoxymethylium methyl sulfate was added dropwise, under nitrogen. The temperature was raised to 20°C and maintained for 6 hrs. To it was added 2 lit. of 2% aq. sodium hydroxide solution and stirred for 10 mm. The organic layer was separated, dried over sodium sulfate and concentrated under reduced pressure to give the product. It was further washed by hexane to give 1.325

kg. of pure, dry 2-propenoic acid, 3- (dimethylamino)-, ethyl ester, (E). m. p.: 44- 46°C.

IR: cm'' in NMR (CDC13,200MHz) 8: 7.43 (d, 1H, J=12.86 Hz), 4.51 (d, lH, J=12.87 Hz), 3.66 (s, 3H), 2.88 (s, 6H) Mass: 129 (95%), 114 (24%), 98 (100%) and 82 (11%).

2-Propenoic acid, 3- (dimethylamino), methyl ester, (E) was also prepared by using sodium salt of malonate.

EXAMPLE 4: Preparation of ethyl potassium malonate by using diethyl malonate.

A 250 ml. round bottom flask was charged with 40 ml. of ethanol under nitrogen. To it was added 20 gm. of diethylmalonate and it was cooled to 5- 20°C, preferably to 10°C. To this cooled solution, ethanolic potassium hydroxide solution (prepared by slow addition of 8 gm. of potassium hydroxide in 30 ml of ethanol under nitrogen) was added. The reaction mixture was stirred for 7 hr. The reaction mixture was then cooled to 0-10°C, preferably to 5°C for 30 mm. The solid which separated out was filtered to give 13 gm. of ethyl potassium malonate.

EXAMPLE 5: Preparation of ethyl potassium malonate by using dimethyl malonate.

A 250 ml. round bottom flask was charged with 40 ml. of ethanol under nitrogen. To it was added 20 gm. of dimethylmalonate and it was cooled to 0-

15°C, preferably to 10°C. To this cooled solution, ethanolic potassium hydroxide solution (prepared by slow addition of 9.9 gm. of potassium hydroxide in 30 ml. of ethanol under nitrogen) was added. The reaction mixture was stirred for 7 hr. The reaction mixture was then cooled to 5°C for 30 mm. The solid which separated out was filtered to give 15 gm. of ethyl potassium malonate.

EXAMPLE 6: Preparation of 2-propenoic acid, 3- (dimethylamino), ethyl ester, (E).

In a 250 ml round bottom flask 10 gm. of ethyl potassium malonate in 40 ml. of ethylene dichloride was added. The reaction mixture was cooled to 5-20°C, preferably to 10°C, and 16 gm of N, N-dimethylamino methoxymethylium methyl sulfate was added dropwise under nitrogen.

The temperature was raised to 20°C and maintained for 6 hrs. To it was added 10 ml of 2% aq. sodium hydroxide solution and stirred for 10 min. The organic layer was separated, dried over sodium sulfate and concentrated under reduced pressure to give 5.5 gm of the product i. e. 2-propenoic acid, 3- (dimethylamino), ethyl ester, (E).