Generation of [1,2,4]triazolo[1,5-a]pyrimidine N-ylides and their ring transformation reactions

Abstract

[1,2,4]Triazolo[1,5-a] pyrimidine (1) has been alkylated at the N(3)-position by treatment with alkyl halides in refluxing dry acetone. The ylides (3) were generated in situ from the iminium salts (2) and 1 equiv. of triethylamine. Thermolysis of the ylides (3) in dry acetonitrile gave the 2-cyanamido-pyrimidines (4). The N(3)-phenylacyliminium salt (2e) when treated with 2 equiv. of triethylamine gave 2-(2-imino-5-phenyl-2,3-dihydro-oxazol-3-yl)pyrimidine (5) in 64.4% yield. The latter on hydrolysis gave the oxazolone (7), and on treatment with nucleophiles such as alcohols or amines under acidic conditions afforded the ring transposition products imidazol-2-ylpyrimidines (8) or (9), respectively. The reaction mechanism for the novel thermolysis of the ylides is discussed.