Catalytic Asymmetric C−H Functionalization under Photoredox Conditions by Radical Translocation and Stereocontrolled Alkene Addition

Abstract

This work demonstrates how photoredox-mediated C(sp )-H activation through radical translocation can be combined with asymmetric catalysis. Upon irradiation with visible light, α,β-unsaturated N-acylpyrazoles react with N-alkoxyphthalimides in the presence of a rhodium-based chiral Lewis acid catalyst and the photosensitizer fac-[Ir(ppy) ] to provide a C-C bond-formation product with high enantioselectivity (up to 97 % ee) and, where applicable, with some diastereoselectivity (3.0:1 d.r.). Mechanistically, the synthetic strategy exploits a radical translocation (1,5-hydrogen transfer) from an oxygen-centered to a carbon-centered radical with a subsequent stereocontrolled radical alkene addition.

Visible‐Light‐Promoted Ring‐Opening Alkynylation, Alkenylation, and Allylation of Cyclic Hemiacetals through β‐Scission of Alkoxy Radicals

“…Chen et al. introduced a visible‐light‐induced generation of alkoxy radicals from N ‐alkoxyphthalimides . More recently, alkoxy radical generation based on the photocatalytic reduction of N ‐alkoxyazinium or azolium salts has been reported .…”

Combining the catalytic enantioselective reaction of visible-light-generated radicals with a by-product utilization system

“…Our design is based on our recently introduced bis-cyclometalated chiral rhodium-based Lewis acids (LAs) 13,14 for the electronic activation of substrates through two-point binding and employs Hantzsch esters ( HE s) 15 as a photoredox mediator for the generation of radical species under mild conditions (Fig. 2).…”

Controllable Remote C−H Bond Functionalization by Visible‐Light Photocatalysis

“…[6] Remarkably,inthis reaction, the two catalysts proved to be well compatible with each other and enabled the formation of the desired adducts in generally good yields and excellent enantioselectivities. Shortly after, Meggers and co-workers also achieved an asymmetric alkylation of remote C(sp 3 ) À Hbonds in N-alkoxy phthalimides 6 with a,b-unsaturated N-acyl pyrazoles 7 by combining their previously developed chiral rhodium-based Lewis acid catalyst (D-RhS) with the photocatalyst fac-Ir(ppy) 3 under visible-light irradiation (Scheme 2b).…”