Ring opening or rearrangement versus N-oxidation in the action of peracids upon pyrrolo[2,3-b]pyridines, pyrrolo[2,3-b]pyrazines, and triazolo[1,5-a]- and triazolo[4,3-a]-pyrazine. Some chemical and spectroscopic properties of the triazolopyrazines and their N-oxides

Abstract

Peracid oxidation of the title heterocycles has shown a variety of reaction pathways. 1-Methyl-2,3-diphenyl-1H-pyrrolo[2,3-b]pyridine (8) gave a ring-opened product (13), while 3-methyl-2-phenyl-1H-pyrrolo[2,3-b]pyrazine gave N-benzoylurea. In contrast, triazolo[1,5-a]pyrazine (36) undergoes smooth N-oxidation to the 7-oxide (37), triazolo[4,3-a]pyrazine (41) gives the N-oxide (42) less efficiently, and the pyrrolopyrazine (26) undergoes rearrangement and N-oxidation to give the spiro-compound (28). Triazolo[4,3-a]pyrazine 7-oxide (42) is readily obtained from 2-hydrazinopyrazine 4-oxide (45). The N-alkylation of the 2,3-diphenyl-1H-pyrrolo[2,3-b]pyridines (5) and (6), certain useful features of the n.m.r. spectra of the triazolopyrazines, (36) and (41), and their N-oxides, and some reactions of these N-oxides are reported.