ONE BICYCLIC BETA-LACTAM AND 2 BICYCLIC GAMMA-LACTAM COMPOUNDS

The crystal structures of tile bicyclic beta-lactam, ethyl-8-oxo-1-aza bicyclo[4.2.0]octane-2-carboxylic acid methyl ester, C10H14ClNO3 (1), and the bicyclic gamma-lactams, rac-(5R, oro-7-methyl-3-oxooctahydroi ndolizine-5-carboxylic acid methyl ester, C11H16ClNO3 (2), and c-(5R, 6S,10R*)-3-oxo-6-vinyloctahydro-1H-pyrrolo [1,2-a]azepine-5-carboxyli c acid methyl ester, C13H19NO3 (3), have been established by X-ray cry stallography. In (1) and (2) the alpha-amino ester function and the Cl atom occupy an axial position in a chair-like piperidine ring. In (3) the methyl ester and the vinyl group are equatorially placed on the c hair-like seven-membered ring. The criteria defined by Foces-Foces, Ca ne & Garcia-Blanco [Acta Cryst. (1976), B32, 3029-3033] to determine t he conformation of a six-membered ring are compared with those defined by Duax, Weeks & Rohrer [Top. Stereochem. (1976), 9, 271-383]. It can be seen that the former cannot be used to determine the conformation of a six-membered ring correctly in the case of strain imposed by a fo ur-membered fused ring such as in (1).