Pentadienyl Type Lithium and Potassium Species: The Regioselectivity of their Reactions with Electrophiles
作者:Manfred Schlosser、Armin Zellner、Frédéric Leroux
DOI:10.1055/s-2001-17521
日期:——
Seven structurally distinct pentadienyl type lithium and potassium compounds were screened against a variety of electrophiles in order to assess the regioselectivity of the trapping reactions. Organoborates and analogs thereof (fluorodimethoxyborane) proved to be perfectly regioreliable attacking only unsubstituted terminal positions and thus providing, after oxidation, exclusively primary allylic alcohols. 2,4-Pentadienyllithiums or -potassiums, that carry a methyl group at the 1- or 3-position, exhibit the same extreme regioselectivity towards halotrialkylsilanes or carbon dioxide. Although the unsubstituted parent compounds combine with such electrophiles still preferentially at the terminal position, considerable proportions of branched products are concomitantly formed as well (1/3-attack ratios ranging from 2:1 to > 20:1). Hydroxyalkylating and alkylating reagents such as formaldehyde, oxirane or butyl iodide invariably afford regioisomeric mixtures generally varying in composition between 3:1 and 1:3. The condensation reaction with halotrialkylsilanes appears to follow a concerted (SN2-like) rather than an addition/elimination (ate complex-mediated) mechanism.
进行了七种结构不同的戊二烯基型锂和钾化合物的筛选,以评估它们与各种亲电试剂反应的区域选择性。有机硼酸盐及其类似物(氟二甲氧基硼烷)显示了非常可靠的区域选择性,仅攻击未取代的末端位置,因此氧化后只得到完全的一级烯丙基醇。带有甲基的2,4-戊二烯基锂或钾在1-或3-位置上,对卤代三烷基硅烷或二氧化碳显示出相同的极端区域选择性。尽管未取代的母体化合物仍优先在末端位置与这些亲电试剂反应,但同时也会生成相当比例的支链产物(1/3-攻击比例从2:1到超过20:1)。羟烷基化和烷基化试剂,如甲醛、环氧乙烷或丁基碘,总是得到区域异构体的混合物,其组成通常在3:1和1:3之间变化。与卤代三烷基硅烷的缩合反应似乎遵循协同(类似SN2)而非加成/消除(通过ate复合体介导)的机制。