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

An efficient and general method for the synthesis of 1,4‐oxazepines is described. When reacted with ZnCl 2 in DCM at 40 °C or CHCl 3 at 61 °C, N ‐propargylic β‐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 β‐enaminones, and proceeds with high efficiency and with broad functional group tolerance. The reactions in refluxing CHCl 3 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.