PURPOSE: To obtain a methyl N -acyl-2-azabicyclo [3,3,0] octane-3 -carboxylate, etc., by radical -cyclizing a methyl 2 -(N -acyl-N -cyclopentenylamino) -3- iodopropionate, etc.

CONSTITUTION: A compd. of formula I [where (n) is 1-3; R is an acyl; R1 is an alkyl, a cycloalkyl, an aralkyl, etc.; Hal is Cl, Br or I] is radical-cyclized with hydrogenated tri-n-butyl tin, etc., at a temp. between 0°C and the b.p. of the reactive mixture in a solvent such as benzene or toluene optionally in the presence of a radical initiator such as t-butyl peroxide to obtain the objective compd. of formula II useful as an inhibitor of Angiotensin Converting Enzyme, etc. The radical cyclization may be carried out at 10-50°C in a dipolar aprotic solvent such as diethyl ether or THF.