One-Pot Synthesis of 2-Acetyl-1H-pyrroles from N-Propargylic ß-Enaminones via Intermediacy of 1,4-Oxazepines.

A one-pot two-step protocol for the synthesis of 2-acetyl-1H-pyrroles from N-propargylic ß-enaminones was described. When treated with zinc chloride in refluxing chloroform, N-propargylic ß-enaminones produced in situ 2-methylene-2,3-dihydro-1,4-oxazepines, which, upon further refluxing in methanol with zinc chloride, afforded 2-acetyl-1H-pyrroles. The process was found to be general for a wide variety of N-propargylic ß-enaminones and yielded a diverse range of 2-acetyl-1H-pyrroles in good to high yields with large substrate scope and good functional group tolerance. This operationally easy method may provide a rapid access to functionalized 2-acetyl-1H-pyrroles of pharmacological interest.