The synthesis of electron donor‐acceptor substituted pyrazoles

A variety of 1,3‐ and 1,5‐donor‐acceptor substituted pyrazole derivatives have been synthesized by the cyclocondensation of α,β‐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. Copyright © 1993 Journal of Heterocyclic Chemistry