Gold-Catalyzed Asymmetric Thioallylation of Propiolates via Charge-Induced Thio-Claisen Rearrangement

A gold­(I)-catalyzed enantioselective
thioallylation of propiolates
with allyl sulfides is described. The key mechanistic element is a
sulfonium-induced Claisen rearrangement which helps minimize the allyl
dissociation and render higher enantioselectivity. This protocol features
remarkable scope of the allyl moiety, allowing enantiocontrolled synthesis
of all-carbon quaternary centers, and exhibits exceptional functional
group compatibility with many Lewis bases and π-bonds. This
intermolecular variant of Claisen rearrangement forges both C–S
and C–C bonds concomitantly, providing efficient access to
interesting optically active organosulfur compounds which can be transformed
further through the vinyl sulfide as a functional handle. The rate
of the reaction was zeroth order with respect to allyl sulfides, which
suggested a reversible inhibition, providing a resting state for the
catalyst. The Hammett plot displayed a correlation with σp values, suggesting a turnover-limiting sigmatropic rearrangement
where decreased electron-density on sulfur accelerated the rearrangement.

本文报道了一例金(I)催化的丙炔酸酯与烯丙基硫醚的对映选择性硫代烯丙基化反应。其关键机理环节为锍鎓盐诱导的克莱森重排（Claisen rearrangement），该重排过程可有效抑制烯丙基解离，从而获得更高的对映选择性。
该反应体系展现出优异的烯丙基片段底物兼容性，可实现全碳季碳中心的对映控制合成，同时对众多路易斯碱与π键表现出极佳的官能团耐受性。
此分子间克莱森重排变体可同时构建C-S键与C-C键，能够高效制备具有应用潜力的手性有机硫化合物，该类化合物可进一步通过乙烯基硫醚这一官能团位点进行后续转化。
反应速率对烯丙基硫醚呈零级反应动力学特征，这表明体系存在可逆抑制作用，为催化剂提供了休眠态。
哈米特图（Hammett plot）与σ_p参数（σp values）呈现良好相关性，提示决速步为σ迁移重排过程，硫原子上电子云密度的降低可加速该重排反应。