Regioselective formation of hydroxy lactams from pyridine-2,3-dicarboximides and their cyclodehydration to pyrido[2′,3′:3,4]pyrrolo-fused heterocyclic systems

Abstract

Grignard reactions of pyridine-2,3-dicarboximides involve attack at the carbonyl group closer to the pyridine nitrogen atom to give 7-hydroxypyrrolo[3,4-b]pyridin-5(7H)-one derivatives. Reduction of the same imides with sodium borohydride gives mixtures of regiosomeric hydroxy lactams, in which the 7-hydroxypyrrolo[3,4-b]pyridin-5-ones are the major components. Hydroxy lactams derived by either of these two methods from pyridine-2,3-dicarboximides containing N-benzyl, N-2-phenylethyl, N-2-(indol-3-yl)ethyl, or N-biphenyl-2-yl substituents are cyclised by heating in trifluoroacetic or polyphosphoric acid to give derivatives of new pyrido[2′,3′:3,4]pyrrolo-fused heterocyclic systems.