A photoredox activation mode of formate salts for carboxylation
was developed. Using a formate salt as the reductant, carbonyl source,
and hydrogen atom transfer reagent, a wide range of alkenes can be
converted into acid products via a carboxyl group transfer strategy
in an additive-free fashion. Mechanistic studies revealed that radical
anion species (CO2
•– and carbon
radical anions derived from the reduction of alkenes) are key intermediates
of the transformation. This method has the advantages of high catalytic
efficiency and a simple catalytic system, which may allow this approach
to become a promising strategy for industrial applications.
In
recent decades, difunctionalization of alkenes has received
considerable attention as an efficient and straightforward way to
increase molecular complexity. However, examples of the difunctionalization
of alkenes initiated by the intermolecular addition of alkoxycarbonyl
radicals providing substituted alkanoates are still rare. Herein,
we present the visible light-driven metal-free divergent difunctionalization
of alkenes triggered by the intermolecular addition of alkoxycarbonyl
radicals under ambient conditions. Employing alkyl formates as precursors
of alkoxycarbonyl radicals and 4CzIPN as the photocatalyst, a variety
of substituted alkanoates, including β-alkoxy, β-hydroxy,
β-dimethoxymethoxy, and β-formyloxy alkanoates, could
be facilely accessed with high functional group tolerance and high
efficiency. Moreover, the mechanism study revealed that β-hydroxy
alkanoates were generated by a selective decomposition of orthoformates
promoted by the N-alkoxyazinium salt.
Copper N-heterocyclic carbene complexes can be readily used as catalysts for both aerobic oxidation of alcohols to aldehydes and reduction of imines to amines. Our methodology is universal for aromatic substrates and shows versatile tolerance to potential cascade reactions. A one-pot tandem synthetic strategy could afford useful imines and secondary amines via an oxidation-reduction strategy.
A photoredox-catalyzed
α-C(sp3)–H activation
approach of unprotected secondary amines is reported. Such transformations
provide facile access to various 1,4-dicarbonyl compounds using readily
available amines and α,β-unsaturated compounds as feedstocks
under air conditions. The substrate scope of this method is broad,
and a wide array of functional groups are tolerated.
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