An expeditious FeCl3-catalyzed cascade 1,4-conjugate addition/annulation/1,5-H shift sequence for modular access of all-pyrano-moiety-substituted chromenes

ortho-Alkynyl quinone methides are well-known four-atom synthons for direct [4 + n] cycloaddition in constructing useful oxa-heterocyclic compounds owing to their high reactivity as well as the thermodynamically favored aromatization nature of this process. Herein we report an operationally simple and eco-friendly protocol for the modular and regioselective access of (E)-4-(vinyl or aryl or alkynyl)iminochromenes from propargylamines and S-methylated beta-ketothioamides in the presence of FeCl3, and particularly under undried acetonitrile and air atmosphere conditions. This method exhibits a broad substrate scope and displays nice functional group compatibility, thus providing an efficient access of 3,4-disubstituted iminochromenes.

Automated summary

An operationally simple and environmentally friendly method for the modular and regioselective synthesis of (E)-4-(vinyl or aryl or alkynyl)iminochromenes from propargylamines and S-methylated beta-ketothioamides using FeCl3 in undried acetonitrile and air atmosphere is reported. This method exhibits a broad substrate scope and nice functional group compatibility, providing an efficient access to 3,4-disubstituted iminochromenes.