One Bicyclic β-Lactam and Two Bicyclic γ-Lactam Compounds

The crystal structures of the bicyclic β-lactam, rac-(2R*,4S*,6S*)-4-chloro-4-methyl-8-oxo-1- azabicyclo­[4.2.0]octane-2-carboxylic acid methyl ester, C₁₀H₁₄ClNO₃, (1), and the bicyclic γ-lactams, rac-(5R*,7S*,9S*)-7-chloro-7- methyl-3-oxooctahydroindolizidine-5-carboxylic acid methyl ester, C₁₁H₁₆ClNO₃, (2) and rac-(5R*,6S*,10R*)-3-oxo-6-vinyloctahydro-1H-pyrrolo[1,2-a]azepine-5-carboxylic acid methyl ester, C₁₃H₁₉NO₃, (3), have been established by X-ray crystallography. In (1) and (2) the α-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 located on a chair-like seven-membered ring. The criteria defined by Foces-Foces, Cano & Garciá-Blanco [Acta Cryst. (1976), B32, 3029–3033] to determine the 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 correctly determine the conformation of a six-membered ring in the case of strain imposed by a four-membered fused ring such as in (1).

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