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

Article abstract of DOI:10.1016/S0040-4039(00)92391-8

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.