Development of Stereoselective Synthetic Reactions Induced by Transition Metal Redox System

频那醇偶联为合成天然化合物中碳-碳键的形成提供了一种通用的方法。低价早过渡金属的氧化还原过程在偶联反应中是有用的，但通常需要超过化学计量的金属还原剂才能完成还原反应。在锌和氯硅烷的存在下，实现了一种新的氧化还原体系用于钒催化的片呐醇偶联反应，高产率地得到了相应的1，2-二醇。氯硅烷的共存对于催化偶联反应是必不可少的。以PhMe_2SiCl生成dl异构体时，具有较高的非对映选择性，在乙酰化试剂如Ac_2O或ACCL的存在下，片呐醇发生催化偶联反应。当芳香醛与VOCl3的摩尔比为3%，Ac_2O的摩尔数为2，以锌粉为助还原剂时，得到的邻二乙酰化二醇具有较高的非对映选择性。TiCl4也可以作为ACCL和金属铝的催化剂。在氯三甲基硅烷存在下，钒催化芳基丙二腈的环二聚反应发生非对映选择性的氧化还原反应。综上所述，在还原偶联反应中开发了一种高效的单电子催化还原体系。

Pinacol coupling provides a versatile method for carbon-carbon bond formation in the synthesis of naturally occurring compounds. Redox process of low-valent early transition metals is synthetically useful in the coupling reaction, but more than stoichiometric amounts of metallic reductants are generally required to accomplish the reduction reaction.A novel redox system for the vanadium-catalyzed pinacol coupling was achieved in the presence of zinc and a chlorosilane to give the corresponding 1,2-diols in high yields. The co-existence of a chlorosilane is essential for the catalytic coupling reaction. The high diastereoselectivity was attained with PhMe_2SiCl to give the dl isomer.Catalytic pinacol coupling reaction took place in the presence of an acetylating reagent such as Ac_2O or AcCl. When aromatic aldehydes are treated with 3mol% of VOCl_3, 2 molar amount of Ac_2O, and zinc powder as a co-reductant, vicinal diacetylated diols were obtained with high diastereoselectivity. TiCl_4 could also be utilized as a catalyst with AcCl and metallic aluminum.A vanadium-catalyzed cyclodimerization of arylidine malononitriles proceeded diastereoselectively with reversible redox between vanadium and zinc in the presnce of chlorotrimethylsilane. In conclusion, an efficient system for catalytic one-electron reduction was developed in reductive coupling reactions.