Department of Chemistry, University of California, Berkeley, California 94720, United States.
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.
J Am Chem Soc. 2021 Sep 1;143(34):13759-13768. doi: 10.1021/jacs.1c05769. Epub 2021 Aug 16.
Herein we report the copper-catalyzed silylation of propargylic difluorides to generate axially chiral, tetrasubstituted monofluoroallenes in both good yields (27 examples >80%) and enantioselectivities (82-98% ee). Compared to previously reported synthetic routes to axially chiral allenes (ACAs) from prochiral substrates, a mechanistically distinct reaction has been developed: the enantiodiscrimination between enantiotopic fluorides to set an axial stereocenter. DFT calculations and vibrational circular dichroism (VCD) suggest that β-fluoride elimination from an alkenyl copper intermediate likely proceeds through a -β-fluoride elimination pathway rather than an -elimination pathway. The effects of the C1-symmetric Josiphos-derived ligand on reactivity and enantioselectivity were investigated. Not only does this report showcase that alkenyl copper species (like their alkyl counterparts) can undergo β-fluoride elimination, but this elimination can be achieved in an enantioselective fashion.
在此，我们报告了铜催化的炔丙基二氟化物的硅化反应，以高产率（27 个实例>80%）和对映选择性（82-98%ee）生成轴手性的四取代单氟烯丙基。与以前报道的从前手性底物合成轴手性烯丙基（ACAs）的方法相比，开发了一种具有不同机制的反应：对映异位氟化物之间的对映选择性消除以设置轴向立体中心。DFT 计算和振动圆二色性（VCD）表明，烯丙基铜中间体中β-氟化物的消除可能通过β-氟化物消除途径而不是消除途径进行。研究了 C1 对称的 Josiphos 衍生配体对反应性和对映选择性的影响。本报告不仅展示了烯丙基铜物种（与它们的烷基对应物一样）可以进行β-氟化物消除，而且可以以对映选择性的方式实现这种消除。
