Synthesis of novel pyrazoles via [2+3]-dipolar cycloaddition using alkyne surrogates

The syntheses of an important class of hitherto unreported novel pyrazoles are described The regioselective synthesis of 1,3,4,5-tetrasubstituted pyrazoles was achieved by the Huisgen cyclization of nitrile imines With a trisubstituted bromoalkene The substituted bromoalkene functions as an alkyne synthon which was used to construct 5,5-disubstituted bromopyrazoline intermediates that undergo aromatization to the analogous pyrazoles through the loss of HBr The cycloaddition regioselectivity was confirmed through single X-ray crystal data of one of the pyrazoles (C) 2010 Elsevier Ltd All rights reserved