1,2‐Diarylethanols by Alternative Regioselective Reductive Ring‐Opening of 2,3‐Diaryloxiranes

Abstract

Abstract Non‐symmetrical trans ‐2,3‐diaryloxiranes have been regioselectively opened by catalytic hydrogenation over Pd/C, NaBH 4 /Pd and [Cp 2 TiCl]/H 2 O. Although in the catalytic hydrogenation reactions the epoxides were mainly opened at the β‐carbon with respect to the substituted aryl ring in all cases, with the [Cp 2 TiCl]/H 2 O system the regioselectivity was affected by the electronic properties of the aryl residues, the epoxides being opened on the carbon bearing the most electron‐releasing or the least electron‐withdrawing group. With the NaBH 4 /Pd system different regioisomers were obtained depending on the substituents. Starting from enantioenriched epoxides, no loss of optical purity was observed in the alcohols formed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)