Reactions of some αβ-unsaturated pyrazolyl compounds with bromine and with grignard reagents

Abstract

The reaction of bromine with 3-(1-phenylpyrazol-4-yl)acrylic acid and its esters has been reinvestigated. and the product has now been shown to be the α- and not the β-bromo-derivative as was believed previously. This has been established by n.m.r. spectroscopy and an elimination–addition mechanism has been suggested to explain the conversion of the α-bromoacrylic acid into the β-keto-acid by alkali. Pyrazolylpropynoic acids and pyrazolylacetylenes have been isolated and hydrated in alkaline solution to β-keto-acids and acetylpyrazoles, respectively. Reactions of Grignard reagents with pyrazolylacrylic esters and pyrazolylprop-2-en-1 -ones have also been studied.