New Intramolecular Five-Endo-Mode Cyclization of Allenyl Aryl Ketones

Abstract
A convenient preparation of allenyl aryl ketones was achieved by the Weinreb-modified Grignard reaction of N-methoxy-N-methylamides with propargylmagnesium bromide. On treatment with BF3·OEt2, the allenyl aryl ketones were converted to methylenebenzocyclopetenones via a new 5-endo-mode cyclization.