The Synthesis of Electron Donor-acceptor Substituted Pyrazoles

Abstract

A variety of 1,3- and 1,5-donor-acceptor substituted pyrazole derivatives have been synthesized by the cyclocondensation of a,b-ethynyl ketones with substituted phenyl hydrazines. The regioselectivity of the cyclization depends on the reaction conditions in a manner consistent with competitive 1,2- and 1,4-addition followed by ring closure. 1,4-Disubstituted derivatives can be prepared from the corresponding 4-iodopyrazole using palladium catalyzed carbon-carbon bond forming reactions. The pyrazole chromophores are expected to show interesting nonlinear optical properties.