The regioselectivity of the formation of 2-pyrazolylthiazoles and their precursors from the reaction of 2-hydrazinothiazoles with 4,4,4-trifluoro-1-hetaryl-1,3-butanediones

  • Denisova A
  • Sosnovskikh V
  • Dehaen W
 et al. 
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Abstract

Reaction of 2-hydrazinothiazoles 1 with 1-thienyl-and 1-furyl-1,3-butanediones 2a,b in methanol in the presence of hydrochloric acid mainly leads to a mixture of pyrazoles 3 and pyrazolines 4 or pyrazoles 3 and 5 in strong acidic conditions. Isomeric hydrazones 6 and pyrazolines 4 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones 2 with hydrazine 1 is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones 2. Cyclization of hydrazones 6 is shown to occur under milder conditions than dehydration for pyrazolines 4. The new heterocyclic compounds were prepared and fully characterized by NMR spectra and by X-ray analysis for 3c. © 2002 Elsevier Science B.V. All rights reserved.

Author-supplied keywords

  • 1-3-Diketones
  • 13C NMR
  • 19F
  • 1H
  • 2-Hydrazinothiazoles
  • Pyrazolythiazoles
  • Regioselectivity

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