ETH Zürich , Vladimir-Prelog-Weg 3, HCI , 8093 Zürich , Switzerland.
Department of Chemistry , University of Toronto , Toronto , Canada , M5S 3H6.
J Am Chem Soc. 2018 Apr 4;140(13):4697-4704. doi: 10.1021/jacs.8b01416. Epub 2018 Mar 22.
An enantioconvergent C(sp)-C(sp) coupling between racemic allenylic electrophiles and alkylzinc reagents has been developed. An Ir/(phosphoramidite,olefin) catalyst provides access to highly enantioenriched allenylic substitution products (93-99% ee) with complete regiocontrol (>50:1 rr in all cases) over the corresponding 1,3-diene isomers which are obtained predominantly when other metal catalysts are emplyed. The synthetic utility of the products obtained was highlighted in a variety of stereoselective transition metal-catalyzed difunctionalization reactions. Furthermore, a combination of experimental and theoretical studies provide support for a putative reaction mechanism wherein enantiodetermining C-C coupling occurs via nucleophilic attack on a highly planarized aryl butadienylium π-system that is coordinated to the Ir center in an η-fashion.
一种对映选择性的 C(sp)-C(sp) 偶联反应，涉及外消旋烯丙基亲电试剂和烷基锌试剂，已经被开发出来。一种 Ir/(膦酰胺配体、烯烃)催化剂可以提供高对映选择性的烯丙基取代产物（93-99%ee），具有完全的区域选择性（在所有情况下 >50:1 rr），而当使用其他金属催化剂时，主要得到相应的 1,3-二烯异构体。所获得的产物的合成实用性在各种立体选择性过渡金属催化的双官能化反应中得到了强调。此外，实验和理论研究的结合为一个假定的反应机制提供了支持，其中决定对映体的 C-C 偶联是通过亲核进攻高度平面化的芳基丁二烯翁π-体系发生的，该体系以η-方式与 Ir 中心配位。
