Synthesis and structural studies of novel fused seven-membered carbocycles derived from exo-2-oxazolidinone dienes through (4+3) cycloadditions

A series of novel, fused seven-membered rings were obtained from (4+3) cycloadditions of diverse exo-2-oxazolidinone dienes and an oxyallyl cation. 2D-NMR studies (COSY, NOESY, HMBC, and HSQC) showed that the fused carbocycles were obtained as endo/exo diastereoisomeric mixtures. The structure of the predominant exo diastereoisomer was unambiguously established for one of the analogues by X-ray crystallography. It is noteworthy that for the N-benzyl diene, a highly exo stereoselective cycloaddition took place to afford a single isomer.

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