Asymmetric
photoredox catalysis offers exciting opportunities to
develop new synthetic approaches to chiral molecules through novel
reaction pathways. Employing the first-row transition metal complexes
as the chiral photoredox catalysts remains, however, a formidable
challenge, although these complexes are economic, environmentally
friendly, and often exhibit special reactivities. We report in this
Article the development of one class of highly efficient asymmetric/photoredox
bifunctional catalysts based on the copper(II) bisoxazoline complexes
(CuII–BOX) for the light-induced enantioselective
alkylation of imines. The reactions proceed under very mild conditions
and without a need for any other photosensitizer. The simple catalytic
system and readily tunable chiral ligands enable a significantly high
level of enantioselectivity for the formation of chiral amine products
bearing a tetrasubstituted carbon stereocenter (36 examples, up to
98% ee). Overall, the CuII–BOX catalysts initiate
the radical generation, and also govern the subsequent stereoselective
transformations. This strategy utilizing chiral complexes comprised
of a first-row transition metal and a flexible chiral ligand as the
asymmetric photoredox catalysts provides an effective platform for
the development of green asymmetric synthetic methods.
The enantioselective photoredox reaction of α,β-unsaturated carbonyl compounds and tertiary/secondary α-silylamines was enabled by a readily available single NiII–DBFOX catalyst under visible light conditions.
The direct and selective C(sp3)-H functionalization of cycloalkanes and alkanes is a highly useful process in organic synthesis owing to the low-cost starting materials, the high step and atom economy. Its application to asymmetric catalysis, however, has been scarcely explored. Herein, we disclose our effort toward this goal by incorporation of dual asymmetric photocatalysis by a chiral nickel catalyst and a commercially available organophotocatalyst with a radical relay strategy through sulfur dioxide insertion. Such design leads to the development of three-component asymmetric sulfonylation involving direct functionalization of cycloalkanes, alkanes, toluene derivatives or ethers. The photochemical reaction of a C(sp3)-H precursor, a SO2 surrogate and a common α,β-unsaturated carbonyl compound proceeds smoothly under mild conditions, delivering a wide range of biologically interesting α-C chiral sulfones with high regio- and enantioselectivity (>50 examples, up to >50:1 rr and 95% ee). This method is applicable to late-stage functionalization of bioactive molecules, and provides an appealing access to enantioenriched compounds starting from the abundant hydrocarbon compounds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.