One pot preparation of pyrido[2,3,4- de]quinazolines and benzo[ de][1,6]naphthyridines by a consecutive process involving an aza-Wittig/electrocyclic ring-closure/heterocumulene-mediated annelation or intramolecular Diels-Alder cycloaddition sequence.

Abstract

Aza Wittig-type reaction of bis(iminophosphorane) 1 with one mole of isocyanate leads to the iminophosphoranes 5 which by treatment with a second mole of isocyanate afforded pyrido[2,3,4-de]quinazolines 6. Similarly, reaction with ketenes leads to the formation of benzo[de][1,6]naphthyridines 9. Direct conversion 1→ 6 and 1→ 9 were achieved using two moles of isocyanate or ketene respectively.