Zinc Chloride Mediated Synthesis of 1,4-Oxazepines from N-Propargylic -Enaminones

An efficient and general method for the synthesis of 1,4-oxazepines is described. When reacted with ZnCl2 in DCM at 40 degrees C or CHCl3 at 61 degrees C, N-propargylic -enaminones undergo 7-exo-dig cyclization to afford 2-methylene-2,3-dihydro-1,4-oxazepines in good to high yields. This cyclization has been found to be general for a diverse range of N-propargylic -enaminones, and proceeds with high efficiency and with broad functional group tolerance. The reactions in refluxing CHCl3 produced 1,4-oxazepines in comparatively short reaction times and with better yields that those obtained in refluxing DCM. This operationally easy method may provide rapid access to a library of functionalized 1,4-oxazepine derivatives of pharmacological interest.