Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama, 700-8530, Japan.
Department of Chemistry, Graduate School of Science, Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
Chemistry. 2019 Nov 27;25(66):15189-15197. doi: 10.1002/chem.201903910. Epub 2019 Oct 30.
A (μ-aryloxo)rhenium complex was isolated and confirmed as a key precatalyst for rhenium-catalyzed ortho-alkenylation (C-alkenylation) of unprotected phenols with alkynes. The reaction exclusively provided ortho-alkenylphenols; the formation of para or multiply alkenylated phenols and hydrophenoxylation (O-alkenylation) products was not observed. Several mechanistic experiments excluded a classical Friedel-Crafts-type mechanism, leading to the proposed phenolic hydroxyl group assisted electrophilic alkenylation as the most plausible reaction mechanism. For this purpose, the use of rhenium, a metal between the early and late transition metals in the periodic table, was key for the activation of both the soft carbon-carbon triple bond of the alkyne and the hard oxygen atom of the phenol, at the same time. ortho-Selective alkenylation with allenes also provided the corresponding adducts with a substitution pattern different from that obtained by the addition reaction with alkynes.
一个（μ-烷氧基）铼配合物被分离出来，并被确认为铼催化未保护酚与炔烃的邻位烯丙基化（C-烯丙基化）的关键前催化剂。该反应仅提供邻烯丙基苯酚；未观察到对位或多烯丙基苯酚和氢苯氧（O-烯丙基化）产物的形成。几种机理实验排除了经典的傅-克型机理，导致提出的酚羟基辅助亲电烯丙基化作为最合理的反应机理。为此，使用铼，一种元素周期表中早期和晚期过渡金属之间的金属，对于同时激活炔烃的软碳-碳三键和酚的硬氧原子是关键。与丙二烯的邻位选择性烯丙基化也提供了与通过与炔烃加成反应获得的取代模式不同的相应加成产物。
