A Silicon Tether Approach for Addition of Functionalized Radicals to Chiral α-Hydroxyhydrazones: Diastereoselective Additions of Hydroxymethyl and Vinyl Synthons
作者:Gregory K. Friestad、Sara E. Massari
DOI:10.1021/jo035405r
日期:2004.2.1
Stereocontrolled additions of hydroxymethyl and vinyl groups to chiral α-hydroxyhydrazones can be achieved by radical cyclizations using bromomethyl or vinyl radical precursors tethered via a temporary silicon connection. Tin-mediated 5-exo radical cyclization of α-hydroxyhydrazones using a silicon-tethered bromomethyl group, followed by oxidative removal of the tether, provides anti-2-hydrazino 1
羟基甲基和乙烯基向手性α-羟基hydr的立体控制加成可以通过使用经由临时硅连接拴系的溴甲基或乙烯基自由基前体的自由基环化来实现。使用硅连接的溴甲基基团,锡介导的α-羟基hydr的5-exo自由基环化,然后氧化脱除该链,可提供高收率的抗-2-肼基1,3-二醇。串联硅烷基乙烯基的α-羟基hydr的串联噻吩基自由基加成环化,然后用氟化钾处理,得到无环烯丙基抗-肼醇的收率很高。巯基加成环化方法已成功扩展到使用α,β-二羟基hydr,而无需事先保护或不进行羟基区分。两种反应类型的非对映选择均随附加基团A值的增加而增加,这与Beckwith-Houk模型对5-己烯基自由基环化中立体控制的预测相符。