Transposition of an Acrylate Moiety in TMSOTf-mediated Reaction of Alkynyl Vinylogous Carbonates Gives Heterocyclic Dienes

TMSOTf-mediated reaction of alkynyl vinylogous carbonates serendipitously gave 1,4-oxazepine and dihydropyran dienes via transposition of an ethyl acrylate moiety involving intramolecular cascade Prins-type cyclization/retro-oxa-Michael reaction/cycloisomerisation. The developed atom-economical protocol selectively provides an E double bond geometry. Dihydropyran dienes could be reduced diastereoselectively using Et3SiH/TMSOTf or could be transformed into polycyclic heterocycles by Heck reaction.