School of Chemistry and Chemical Engineering, Shaanxi Normal University (SNNU), Xi'an, 710062, China.
Institute of Molecular Science and Engineering, Institute of Frontier and Interdisciplinary Sciences, Shandong University, Qingdao, 266237, China.
Angew Chem Int Ed Engl. 2020 Dec 7;59(50):22706-22713. doi: 10.1002/anie.202010832. Epub 2020 Oct 7.
We report chiral Rh cyclopentadienyl-catalyzed enantioselective synthesis of lactams and isochromenes through oxidative [4+1] and [5+1] annulation, respectively, between arenes and 1,3-enynes. The reaction proceeds through a C-H activation, alkenyl-to-allyl rearrangement, and a nucleophilic cyclization cascade. The mechanisms of the [4+1] annulations were elucidated by a combination of experimental and computational methods. DFT studies indicated that, following the C-H activation and alkyne insertion, a Rh alkenyl intermediate undergoes δ-hydrogen elimination of the allylic C-H via a six-membered ring transition state to produce a Rh enallene hydride intermediate. Subsequent hydride insertion and allyl rearrangement affords several rhodium(III) allyl intermediates, and a rare Rh η ene-allyl species with π-agostic interaction undergoes SN '-type external attack by the nitrogen nucleophile, instead of C-N reductive elimination, as the stereodetermining step.
我们报告了手性 Rh 环戊二烯基催化的通过氧化 [4+1] 和 [5+1] 环加成反应，分别从芳基和 1,3-烯炔之间对内酰胺和异色满进行对映选择性合成。该反应通过 C-H 活化、烯基到烯丙基重排和亲核环化级联进行。通过实验和计算方法的结合，阐明了 [4+1] 环加成反应的机理。DFT 研究表明，在 C-H 活化和炔烃插入之后，Rh 烯基中间体通过六元环过渡态经历 δ-氢消除烯丙基 C-H，生成 Rh 烯丙基氢化物中间体。随后的氢化物插入和烯丙基重排得到几种铑 (III) 烯丙基中间体，而罕见的 Rh η 烯-烯丙基物种具有 π-螯合相互作用，通过氮亲核试剂进行 SN '型外部攻击，而不是 C-N 还原消除，作为立体决定步骤。
