Diastereoselective Synthesis of Chromeno[3,2- d ]isoxazoles via Brønsted Acid Catalyzed Tandem 1,6-Addition/Double Annulations of o -Hydroxyl Propargylic Alcohols.

A Brønsted acid catalyzed tandem process to access densely functionalized chromeno[3,2- d ]isoxazoles with good to excellent yields and diastereoselectivities was disclosed. The procedure is proposed to involve a 1,6-conjugate addition/electrophilic addition/double annulations process of alkynyl o -quinone methides ( o -AQMs) in situ generated from o -hydroxyl propargylic alcohols with nitrones. Mild conditions, good functional group compatibility, easy scale-up of the reaction, and further product transformation demonstrated its potential application.