THE SYNTHESIS OF ELECTRON DONOR-ACCEPTOR-SUBSTITUTED PYRAZOLES

A variety of 1,3- and 1,5-donor-acceptor substituted pyrazole derivati ves have been synthesized by the cyclocondensation of alpha,beta-ethyn yl ketones with substituted phenyl hydrazines. The regioselectivity of the cyclization depends on the reaction conditions in a manner consis tent 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 rea ctions. The pyrazole chromophores are expected to show interesting non linear optical properties.