Cyclic hemiaminal formation in some N-unsubstituted azole aldehydes

Abstract

Cyclic hemiaminal formation in solid X-unsubstituted azole aldehydes seems to be a general phenomenon when stabilization factors and position of substitution are favourable. Previously reported for 5- substituted 1,2,4-triazole-3-carbaldehydes and benzimidazole-2- carbaldehyde, it has been found to occur also in some previously undescribed aldehydes of pyrazole, imidazole, 3H-imidazo[4,5- b]pyridine, 3H-imidazo[4,5-c]pyridine, and purine. In purine-8- carbaldehyde the hemiaminal may be accompanied by the aldehyde hydrate. P.m.r. studies of the dimers, and of the dipiperidino cyclic aminals derived from them, indicate that in some cases more than one isomeric form is present.