Enamine catalysis is a prevalent strategy for the functionalization of aldehydes/ketones with electrophiles. Recently, the advent and development of oxidative enamine catalysis have allowed for the coupling of enamines with readily available nucleophiles under oxidative conditions, significantly expanding the domain of typical enamine catalysis. In this perspective, we summarize the recent advances in asymmetric oxidative enamine catalysis. On the basis of the oxidative strategy, these could be classified as (1) oxidation of nucleophile, (2) oxidation of enamine via single-electron transfer (SOMO catalysis), and (3) oxidation of enamine to α,β-unsaturated iminium ion, i.e. oxidative iminium catalysis. These strategies have enabled efficient oxidative functionalizations of aldehydes/ketones with various O-, N-, and C-centered nucleophiles in a highly stereocontrolled manner.
We report herein a direct unsymmetric coupling and controllable aromatization reaction of saturated N-heterocycles enabled by synergistic photoredox and acid catalysis. The reaction furnishes C2−C3 connected biheterocycles in a highly chemo-and regioselective manner under rather mild conditions. Mechanistic studies indicated that the reaction proceeded via enamine-iminium coupling leading to exclusively C2−C3 connection.
We report herein an asymmetric C–H
dehydrogenative allylic
alkylation by a synergistic catalytic system involving a chiral primary
amine, a photoredox catalyst, and a cobaloxime cocatalyst. The ternary
catalytic system enables the coupling of β-ketocarbonyls and
olefins with good yields and high enantioselectivities. Mechanism
studies disclosed a cooperative radical addition process with a chiral
α-imino radical and Co(II)-metalloradical wherein the chiral
primary aminocatalyst and the cobaloxime catalyst work in concert
to control the stereoinduction.
Photocatalytic carboxylic radical aromatic substitution enables the synthesis of diversely substituted coumarins by inert C–X bond cleavage under mild conditions.
An electrochemical strategy has been developed for radical arene carbon–oxygen bond formation. This reaction utilizes DDQ as a redox mediator, with inexpensive glassy carbon electrodes to facilitate an intramolecular lactonization of biphenyl-2-carboxylic acid derivatives via aromatic carboxyl radical substitution to give 6H-benzo[c]chromen-6-ones.
We report herein a catalytic asymmetric dehydrogenative cross-coupling reaction between enones and tertiary amines enabled by synergistic photoredox and chiral primary amine catalysis. The reaction was proposed to proceed via the interception of iminium ion intermediate, in situ generated from photoredox oxidation, by dienamine at α-position, following by isomerization, leading to aza-Morita-Baylis-Hillman-type products with good diastereo- and enantio- selectivity.
We report herein a 1,3-dipolar cycloaddition between enones and nitrones with good to excellent distereo-and enantioselectivities by a chiral primary amine catalyst, which furnishes an operationally simple synthetic protocol for the fused bicyclic isoxazolidine derivatives with multiple stereogenic centers.
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