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

Bromine-lithium exchange using tert-butyllithium at -78 degreesC 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.