A Convenient Route for the Synthesis of Novel 2-Substituted [1,2,4]Triazolo[1,5-c]pyrimidine Derivatives

Abstract

Reactions of easily accessible chloropyrimidinyl hydrazones with bromine were investigated. Oxidative cyclization followed by concomitant bromination led to the formation of [1,2,4]triazolo[4,3-c]pyrimidines, which then underwent the Dimroth rearrangement to afford highly functionalized 2-substituted [1,2,4]triazolo[1,5-c]pyrimidines. Pyrimidines and fused bi-or tricyclic analogues are privileged heterocycles that are of immense importance in the design and discovery of new compounds for pharmaceutical and herbicide applications. 1 In particular, compounds carrying a [1,2,4]triazolo[1,5-c]pyrimidine nucleus have received considerable attention due to their remarkable adenosine and benzodiazepine receptor affinity. 2 For example, 3-and/or 5-substituted 7H-pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines have been reported to be potent xanthine oxidase (XO) inhibitors. 3 Many 1,2,4-triazolo[1,5-c]pyrimidines as well as pyrazolo[4,3-e][1,2,4]triazolo [4,3-c]pyrimidines have recently been prepared and investigated for use as selective antagonists at the A2a receptor, which offers great promise in the treatment of Parkinson's disease. 4 A recent paper by Clarkson and co-workers also predicted the potential use of triazolopyrimidines as inhibitors of Shiga toxin trafficking. 5 In addition, various triazolopyrimidines have been used as the new pharmacological tool for the characterization of human A 3 adenosine receptor. 6

IBD-mediated oxidative cyclization of pyrimidinylhydrazones and concurrent Dimroth rearrangement: Synthesis of [1,2,4]triazolo[1,5-c]pyrimidine derivatives

“…The required starting 4,6-dihydroxypyrimidines 1 can be prepared following the reported procedure by condensation of dimethyl malonate either with formamide (for 1a ) or the respective formamidine salts (for 1b and 1c) [15]. …”

“…Recently, we have reported the synthesis of 8-bromo-7-chloro-[1,2,4]triazolo[1,5- c ]pyrimidines from the reaction of pyrimidinylhydrazones with bromine followed by Dimroth rearrangement [15]. In the present paper, we wish to report an efficient synthesis of new [1,2,4]triazolo[1,5- c ]pyrimidine derivatives from hypervalent iodine (IBD)-mediated oxidative cyclisation of aldehyde pyrimidinylhydrazones and consecutive Dimroth rearrangement in relatively good yields under very mild conditions.…”