Diastereoselective Friedel−Crafts Alkylation of Indoles with Chiral α-Phenyl Benzylic Cations. Asymmetric Synthesis of <i>Anti</i>-1,1,2-Triarylalkanes
作者:John Y. L. Chung、Danny Mancheno、Peter G. Dormer、Narayan Variankaval、Richard G. Ball、Nancy N. Tsou
DOI:10.1021/ol800858c
日期:2008.7.17
The reactions of chiral benzyl carbocations bearing alpha-phenyl substituents with N-sulfonylated indoles afford 1,1,2-triarylalkanes with anti-selectivities. This outcome is a reversal of facial diastereoselectivity relative to Bach's alpha-alkyl-bearing benzyl cations. The reactions are promoted by either a Bronsted acid (TFA) or Lewis acid (BF3.OEt2), offering differential diastereoselectivities
带有α-苯基取代基的手性苄基碳阳离子与N-磺酰化吲哚的反应得到具有反选择性的1,1,2-三芳基烷烃。这一结果是相对于巴赫的含α-烷基苄基阳离子的面部非对映选择性的逆转。布朗斯台德酸(TFA)或路易斯酸(BF3.OEt2)促进反应,提供不同的非对映选择性和反应性。两种反应伙伴的电子性质都强烈影响反应速率和产物非对映选择性,并且似乎在动力学控制下起作用。这种化学性质提供了空间拥挤的四取代乙烷的有效途径。