Regioselective halide attack on 2,3-epoxyalcohols by complex metal halides

Owing to the importance of Sharpless epoxidation reaction in asymmetric synthesis,the regio-and stereoselective opening of the resulting 2, 3-epoxyalcohols has become a topicof current interest.Although many nucleophiles attack Cin high selectivity under the actionof Ti（OR）4,some of them like halides, azide, and cyanide only show moderate propensity