Enantioselective Synthesis of Thiazolopyran Derivatives via a Direct Vinylogous Michael–oxa-Michael Sequence

An efficient diastereo- and enantioselective direct vinylogous Michael–oxa-Michael sequence between 5-alkenyl thiazolones and isopropylidene oxindoles has been developed. The reaction is catalyzed by a bifunctional squaramide catalyst that allows to access a wide range of densely substituted thiazolopyran derivatives containing a quaternary stereocenter. This protocol is flexible toward different sterically and electronically tuned substrates and is amenable to gram-scale synthesis and several synthetic transformations.