Hydride transfer versus electron transfer in the reduction of 4-phenyl-3-halo-3-buten-2-ones mediated by Pichia stipitis

Reductions of (Z)-C6H5CHCXC(O)CH3 (X = Cl, Br) mediated by Pichia stipitis gave 4-phenylbutan-2-one through dehalogenation of intermediaries 3-halo-4-phenylbutan-2-one by an electron transfer mechanism. The addition of 1,3-dinitrobenzene avoids the dehalogenation and thus the corresponding (2S,3S)-halohydrins were obtained in excellent enantiomeric excesses by a hydride transfer mechanism. Irganox® 1010 and 1076 were also used to inhibit the electron transfer mechanism. The obtained halohydrins are important chiral building blocks to obtain optically active epoxides and aminoalcohols.