A new synthesis of substituted pyrazoles from 1,4‐dianions of phenylhydrazones having an α‐hydrogen

Abstract

Abstract The 1,4‐dianions of acetophenone, para ‐substituted acetophenones, deoxybenzoin and dibenzyl ketone phenylhydrazone were prepared by treatment of the respective phenylhydrazone with two molecular equivalents of n ‐butyllithium in tetrahydrofuran‐hexane at 0° and condensed with a variety of aromatic esters, followed by acid cyclization to give the substituted pyrazole in good yield. The synthesis procedure appears to be a convenient and unequivocal method for preparing a particular pyrazole isomer without interfering side reactions. The 1,4‐dianion of N,N ‐diphenylsemicarbazone was also prepared, and the condensation‐cyclization gave the pyrazole in somewhat lower yield.