Isomerizations Akin to the Dimroth Rearrangement. V. Bis-s-triazolo[4,3-α:4',3'-c]pyrimidines and Related Systems

Abstract

Synthetic routes to the parent compounds and/or simple methylated derivatives of bis-s-triazolo[4,3-a:4',3'-c]pyrimidine (1), bis-s-triazolo[l,S-a:4',3'-clpyrimidine (2) and bis-s-triazolo[4,3-a:1',5-c]- pyrimidine (3) are reported. Structures are confirmed by unambiguous syntheses and/or N.M.R. spectral comparisons with known s-triazolo[4,3-a]pyrimidines and their [1,5-a], [4,3-c] and [1,5-c] isomers. Several ill-based structural assignments in the literature are corrected or confirmed. The systems (1)-(3) are unexpectedly stable towards rearrangement in acid or alkali but system (1) does undergo a thermal Dimroth-like rearrangement into system (2). Attempts to prepare an abnormal bis-s-triazolopyrimidine, e.g. (13), from pyrimidine-4,6-diyldihydrazine (12a) are shown to yield only intermediates for, or a degradation product from, the postulated system.