Synthesis of pentacyclic 13-azadibenzo[a,de]anthracenes via anionic cascade ring closure

J Org Chem. 2003 May 16;68(10):4091-2. doi: 10.1021/jo0300340.

Abstract

Bromine-lithium exchange using tert-butyllithium at -78 degrees C initiates a cascade process whereby either xanthone derivatives or pentacyclic 13-azadibenzo[a,de]anthracenes are produced in high yields. The reaction proceeds via a sequential intramolecular trapping of organolithium intermediates.