The preparation of <i>N</i>‐carboalkoxypyrazoles and <i>N</i>‐phenylpyrazoles from C(α)‐dianions of carboalkoxyhydrazones and phenylhydrazones

Abstract

Abstract The 1,4‐dianions of C(α), N ‐carboalkoxyhydrazones and C(α), N ‐phenylhydrazones were prepared in an excess of lithium diisopropylamide (LDA). These dilithiated intermediates resulted from metalation of substituted hydrazones of several all‐aliphatic cyclic ketones, aliphatic‐aromatic cyclic ketones phenylacetaldehyde, and several substituted propiophenones or acetophenones. The esters utilized for Claisen‐type condensations of these dianion intermediates included methyl salicylate, methyl p ‐hydroxybenzoate, methyl nicotinate and related materials. The condensations were followed by acid‐cyclizations to give a variety of N ‐phenylpyrazoles and N ‐carboalkoxypyrazoles, most of which are new.