Synthesis of Benzopyrone-Fused Hydrobenzo[c,d]indoles via Cascade Annulation of p-Quinamines and 3-Formylchromones

Abstract

A 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-catalyzed cascade annulation reaction between p-quinamines and 3-formylchromones was developed, affording a series of benzopyrone-fused hydrobenzo[c,d]indoles in moderate to high yields with excellent diastereoselectivity. This cascade reaction is efficient since two new rings as well as one C–N, one CC, and two C–C bonds are created in a single step. The scale-up synthesis and versatile transformations of the products further demonstrated the practicality and utility of this approach.