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Synthesis of [1,2,4]-triazolo[1,5-a]pyrimidines by Dimroth rearrangement of [1,2,4]-triazolo[4,3-a]pyrimidines: A theoretical and NMR study

Abstract:

Novel [1,2,4]-triazolo-[1,5-a]pyrimidine derivatives were prepared by oxidative cyclization of suitable N-benzylidene-N′-pyrimidin-2-yl hydrazine precursors, followed by a Dimroth rearrangement. Reaction of 6-bromo-[1,2,4]-triazolo-[4,3-a]pyrimidines with aliphatic amines under microwave irradiation gave the unexpected 5-amino compounds from an ANRORC-type mechanism. Full NMR and HRMS characterization was done for all the obtained compounds. DFT calculations of absolute shielding permitted to pbkp_redict 1H, 13C and 15N chemical shifts, which were in good agreement with the experimental ones. Theoretical studies at the B3LYP/6-311++G(d,p) level corroborated that [1,2,4]-triazolo-[1,5-a]pyrimidines were more stable than their [4,3-a] counterparts. © 2010 Elsevier B.V. All rights reserved.