Phosphine-Catalyzed Dual Umpolung Domino Michael Reaction: Facile Synthesis of Hydroindole- and Hydrobenzofuran-2-Carboxylates

A highly
atom-economical, chemoselective, and stereoselective Lewis
base (LB)-catalyzed dual umpolung domino Michael reaction between
cyclohexadienones and alkynyl esters has been developed. PPh3, as a LB catalyst, afforded either the hydroindole-2-carboxylates
or hydrobenzofuran-2-carboxylates 3 as a single diastereomer
in high yields (up to 89%). An obtained product could be easily transformed
to a (S*,S*,R*)-octahydroindole-2-carboxylic acid
((S*,S*,R*)-Oic) analogue.