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

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.