Heterocycles [c]-Fused onto indoloquinoxaline. Synthesis of novel pyrano[2',3':4,5]indolo[2,3-b]quinoxalin-2-ones

摘要

A synthesis of 4-methylpyrano[2,3-e]indole-2,8,9-trione (5) is achieved from 7-amino-4- methylcoumarin by adopting the classical Sandmeyer methodology. The cyclocondensation reaction of pyrano-isatin 5 with the appropriately substituted o-phenylenediamines 6 in polyphosphoric acid proceeded regioselectively to furnish the respective pyrano[2',3':4,5]indolo[2,3-b] quinoxalines 7a - c. Structural assignments of the new compounds are based on microanalytical and spectral (IR, MS and NMR) data.