Lewis Base-Catalyzed Intramolecular Vinylogous Aldol Reaction and Chemoselective Syntheses of 3-Hydroxy-2,3-Disubstituted Dihydrobenzofurans and Indolines.

A Lewis base-catalyzed intramolecular vinylogous aldol reaction of o -(allyloxy)phenyl ketoesters or o -(allylamino)phenyl ketoesters has been developed. This reaction provides ready access to 3-hydroxy-2,3-disubstituted dihydrobenzofurans and indolines in high yields with excellent chemoselectivity and diastereoselectivity. An acid-promoted dehydration of such products further extends the utility of the reaction to the synthesis of 2-alkenyl benzofurans and indoles.