Synthesis and rearrangements of imidazolo- and triazolo-diazines

Document Type

Article

Publication Date

1-1-1989

Abstract

3-Methylimidazolo[1,5-a]pyridine and 3-methyl-1,2,4-triazolo[4,3-a]-pyrazine were prepared by coupling ethyl dithioacetate with 2-(aminomethyl)-pyridine and 2-hydrazinopyrazine, respectively. Both compounds are stable in dilute acids and bases, unlike 3-methyl-1,2,4-triazolo[4,3-a]pyrimidine obtained by coupling the same dithioacetate with 2-hydrazinopyrimidine, which quickly undergoes a Dimroth type rearrangement. Coupling ethyl dithioacetate with 2-hydrazino-4-hydroiy-6-methylpyrimidine yielded a mixture of 3,5-dimethyl-1,2,4-triazolo [4,3-a]-7(8H)-pyrimidone and 3,7-dimethyl-1,2,4-triazolo[4,3-a]-5(8H)-pyrimidone, which were identified by 2D nmr. The last compound underwent a Dimroth rearrangement with acids to yield 2,5-dimethyl-1,2,4-triazolo[1,5-a]-7(4H)-pyrimidone whereas the first did not. Finally, coupling ethyl dithioacetate with 5-chloro-4-hydrazinopyrimidine afforded 8-chloro-3-methyl-1,2,4-triazolo[4,3-c]pyrimidine, which upon treatment with acids underwent a reversible ring opening to afford 2-chloro-1-formamido-2-(5-methyl-1,3,4-triazolo-2-yl)ethene. The latter on pyrolysis gave the starting base without undergoing rearrangement. © 1989.

Publication Title

Heterocycles

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