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

A 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-catalyzed cascade annulation reaction between -quinamines and 3-formylchromones was developed, affording a series of benzopyrone-fused hydrobenzo[,]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.