Synfacts 2007(9): 0913-0913  
DOI: 10.1055/s-2007-968902
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart · New York

Diazafulvenium Methides in Synthesis of Functionalized Pyrazoles

Contributor(s): Victor Snieckus, Toni Rantanen
T. M. V. D. Pinho e Melo*, C. M. Nunes, M. I. L. Soares, J. A. Paixão, A. M. Beja, M. R. Silva
University of Coimbra, Portugal
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Publication History

Publication Date:
23 August 2007 (online)


New chemistry of diazafulvenium methide species, generated by pyrolytic or solution-phase SO2-extrusion from 2,2-dioxo-1H,3H-pyrazolo[1,5-c][1,3]thiazoles, is reported. Two types of reactions, one involving an [8+2] cyclo­addition with different dipolarophiles and the other, a sigmatropic [1,8]-H shift lead to a range of pyrazolo-annulated heterocycles and simple N-vinyl-1H-pyrazoles and C-vinyl-1H-pyrazoles, respectively. The starting pyrazolothiazoles are read­ily prepared from thiazolidine precursors, albeit in low overall yields. The yields of the cycloaddition reactions range from moderate to excellent, while the pyrazole products resulting from hydrogen shifts are obtained in good to excellent yields.