Designing Newα,β-Unsaturated Thioesters for the Catalytic, EnantioselectiveFriedelCrafts Alkylation of Indoles
作者:Marco Bandini、Alfonso Melloni、Simona Tommasi、Achille Umani-Ronchi
DOI:10.1002/hlca.200390317
日期:2003.11
A new class of α,β-unsaturated S-(1,3-benzoxazol-2-yl) thioesters of type 2 have been synthesized and effectively employed as electrophiles in the stereoselective alkylation of indoles. The combination of electronic as well as steric properties of such Michael acceptors allowed us to carry out FriedelCrafts alkylations of various substituted indoles in the presence of a catalytic amount (20 mol-%)
一类新的α,β不饱和小号- (1,3-苯并恶唑-2-基)型的硫酯2已被合成并有效地用作在吲哚的烷基化立体选择性电体。这种迈克尔受体的电子和空间特性的结合使我们能够在催化量(20摩尔%)的手性阳离子[Pd II(Tol-binap)]配合物存在下,进行各种取代的吲哚的FriedelCrafts烷基化反应。。通过优化的催化体系(PdCl 2(MeCN)2 / Tol-binap / AgSbF 6),所需的β以高收率获得-吲哚基取代的硫代衍生物4,对映体过量(ee)最高达86%。通过在温和条件下将它们定量转化为旋光性β-吲哚基酯和酰胺,可以证明对映体富集的硫酯4具有非凡的多功能性。通过这种立体选择性催化FriedelCrafts反应,我们开辟了通往新的α- β-不饱和化合物的道路,这些化合物可能适合制备许多光学活性的β-取代的羧酸化合物。