Enantioselective synthesis of densely functionalized pyranochromenes via an unpredictable cascade Michael-oxa-Michael-tautomerization sequence

摘要

A surprising example of enantioselective cascade Michael-oxa-Michael- tautomerization reactions of malononitrile and benzylidenechromanones has been developed. In this case, malononitrile functions as both nucleophile and electrophile. Meanwhile, a simple bifunctional indane amine-thiourea catalyst has been discovered to promote this process to afford high yields (up to 99%) and high to excellent enantiomeric excesses (81-99% ee).