L-menthyl esters of α-bromomercuryphenylacetic acid: diastereoisomeric purity, symmetrization and reverse reaction. A stereochemical reinvestigation

Abstract

A new experimental procedure for isolation of L-menthyl esters of α-bromo mercuryphenylacetic acid as almost pure diastereoisomers I, [α] 20 D -- 132° and II, [α] 20 D -- 18° is reported. Related dialkylmercuries R 2Hg III, [α] 20 D − 32°, and IV, [α] 20 D − 5°, were prepared. Absolute configurations of benzylic chiral carbon are assigned from ORD curves ( R for I, S for II). S E2 type cleavage of III and IV with mercuric bromide affords I and II, respectively, with expected retention of configuration. 1H NMR spectra (180 MHz) permit distinction between diastereomers I and II and quantitative evaluation of diastereomeric purity. A remarkable influence of solvent on the R 2Hg spectra was observed.