meta- Rather thanortho-Directed Metalations: Buttressing Effects Prejudicing the Proton Abstraction from (2,6-Dihalophenyl)silanes
作者:Christophe Heiss、Fabrice Cottet、Manfred Schlosser
DOI:10.1002/ejoc.200500553
日期:2005.12
neighboring chlorine atoms, it facilitates the permutational displacement of one of them against lithium, a side reaction which occurs whenever alkylithium compds. are employed. At the same time it impedes the attack of hydrogen atoms by the base in the immediate vicinity of the halogens due to relay transmission of steric hindrance. As a consequence, deprotonation occurs preferentially or exclusively
(2,6-二氯苯基)三甲基-和-三乙基硅烷对强碱表现出非典型的反应模式。当用 2,2,6,6-四甲基哌啶锂在 -100 摄氏度下处理时,它们会产生两种,仲丁基或叔丁基锂,甚至三种不同的有机金属中间体,它们可以被标准物质截获。亲电试剂。三烷基甲硅烷基在两个方面介入。对相邻的氯原子施加空间压力,它促进其中一个原子对锂的置换置换,这是一种副反应,每当烷基锂化合物时就会发生。受雇。同时,由于空间位阻的中继传输,它阻止了紧邻卤素的碱对氢原子的攻击。作为结果,去质子化优先或仅发生在 5-(qmetaq) 而不是 4-(qorthoq) 位置。4-锂化物种,作为副产品或 sep 产生。通过置换卤素/金属互变,在 -75 摄氏度下消除氯化锂以释放被芳基锂前体捕获的二脱氢苯 (qarynesq)。[在 SciFinder (R) 上]