Department of Chemistry, Nankai University, Tianjin, 300071, PR China.
J Am Chem Soc. 2013 Jun 26;135(25):9271-4. doi: 10.1021/ja4036785. Epub 2013 Jun 14.
The mechanism of Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enyne (ACE) and alkynes is investigated using density functional theory calculations. The catalytic cycle involves 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes (VCPs), in which alkyne inserts into a rhodium-allyl bond, alkyne insertion into a Rh-C(sp(2)) bond is preferred. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity. In the regioselectivity-determining alkyne insertion step, the alkyne substituent prefers to be distal to the forming C-C bond and thus distal to the OAc group in the product.
使用密度泛函理论计算研究了 Rh 催化的 3-酰氧基-1,4-烯炔（ACE）和炔烃的（5+2）环加成反应的机理。催化循环包括 1,2-酰氧基迁移、炔烃插入和还原消除，以形成环庚三烯产物。与乙烯基环丙烷（VCP）的（5+2）环加成反应不同，在后者中，炔烃插入到铑-烯丙基键中，而炔烃插入到 Rh-C(sp(2))键中是优选的。发现 1,2-酰氧基迁移是催化循环的速率决定步骤。富电子的对二甲氨基苯甲酸酯底物促进 1,2-酰氧基迁移并显著增加反应性。在决定区域选择性的炔烃插入步骤中，炔烃取代基优先位于形成的 C-C 键的远端，因此在产物中位于 OAc 基团的远端。
