NEW MATERIAL:Compounds of formula I (R1 and R2 are H, lower alkyl; A is lower alkylene).

EXAMPLE: 2-Methacryloylcyclopentanecarboxylic methyl ester.

USE: Synthetic intermediate of medicine which is used as remedy or diagnostic for hyperpiesia relating to angiotensin.

PREPARATION: The addition reaction of a compound of formula III to a compound of formula II is effected in the presence of a base to give a compound of formula IV. The hydrolysis of the product gives a compound of formula V, which is subjected to the Mannich reaction together with formaldehyde and an amine of the formula: HNR4R5 (R4 and R5 are H, lower alkyl) to give a compound of formula VI. Then, the product is treated with heat or base to effect deamination, thus producing the compound of formula I. When R1 is lower alkyl, the hydrolysis gives another compound of formula I bearing H as R1.