Stereochemistry of the Allylation and Crotylation Reactions of α-Methyl-β-hydroxy Aldehydes with Allyl- and Crotyltrifluorosilanes. Synthesis of <i>anti,anti</i>-Dipropionate Stereotriads and Stereodivergent Pathways for the Reactions with 2,3-<i>anti-</i> and 2,3-<i>syn</i>-α-Methyl-β-hydroxy Aldehydes
作者:Sherry R. Chemler、William R. Roush
DOI:10.1021/jo0267908
日期:2003.2.1
experiments performed with beta-hydroxy aldehydes 37a (anti) and the corresponding p-methoxybenzyl (PMB) ether 48, and between aldehyde 39 (syn) and the PMB ether 90, established that the 2,3-anti-beta-hydroxy aldehydes react predominantly through bicyclic transition states while the 2,3-syn aldehydes react predominantly through conventional Zimmerman-Traxler transition states. NMR studies established that
描述了一种通过α-甲基-β-羟基醛与(Z)-巴豆基三氟硅烷(24)反应立体合成抗,反二丙酸酯立体三单元体的新方法。这些反应被设计为通过双环过渡态(例如31)发生,其中硅烷试剂与醛的β-羟基共价结合,巴豆基分子内转移。该方法用于合成锌卟啉的C(7)-C(16)区段(58),其中包含合成上具有挑战性的全抗立体五单元。令人惊讶地,2,3-抗-和2,3-syn-α-甲基-β-羟基醛以立体发散的方式与24:2,3-抗-β-羟基醛反应,得到目标的抗,抗二丙酸酯加合物具有高选择性,但是2的反应 3-syn-β-羟基醛的选择性较差。在与烯丙基-(68)和(E)-巴豆基三氟硅烷(27)的反应中,还显示出2,3-顺式对2,3-反-α-甲基-β-羟基醛的立体发散行为。用β-羟基醛37a(抗)和相应的对甲氧基苄基(PMB)醚48以及醛39(syn)和PMB醚90之间进行竞争实验,确定了2,3-抗β-羟基醛主要通过双环过渡态进行反应,而2