An unprecedented radical cross‐coupling reaction was achieved between glycine esters and racemic α‐bromoketones catalyzed by synergistic Brønsted acid/photoredox catalysis, thus serving as an efficient platform for the synthesis of highly valuable enantioenriched unnatural α‐amino acid derivatives. This dual catalysis provides a powerful capability to control the reactive radical intermediate and iminium ion, thereby enabling enantioconvergent bond‐formation in a highly stereochemical manner. An array of valuable enantioenriched unnatural α‐amino acid derivatives bearing two contiguous stereogenic centers are readily accessible with high diastereoselectivity and excellent enantioselectivity, which include α‐amino acids with a unique β‐fluorinated quaternary stereocenter or its β‐all‐carbon counterpart. A strong chiral amplification effect was observed in this dual catalytic system.
An NHC-catalyzed asymmetric [4 + 2] annulation of isatins and α,β-unsaturated carboxylic acids bearing γ-H gave spirocyclic oxindole-dihydropyranones successfully via an in situ activation strategy. This protocol featured easy availability of raw materials, good yields and excellent enantioselectivities (up to 99% ee).
The first de novo construction of enantioenriched dihydroquinazolinones via an intermolecular strategy has been established. This approach also represents the first catalytic asymmetric [4+2] cycloaddition of vinyl benzoxazinanones with sulfonyl isocyanates.
Herein, a novel strategy for the catalytic asymmetric
synthesis
of enantioenriched 3-cis- and 3-trans-substituted prolines has been successfully established via an unprecedented
cascade radical addition/cyclization enabled by synergistic photoredox/Brønsted
acid catalysis and subsequent base-assisted epimerization. The current
protocol provides a unique de novo access to all
four stereoisomers of 3-substituted prolines which are not readily
achieved via currently established methods. This methodology could
be further extended to the asymmetric synthesis of the full complement
of stereoisomers of 3-substituted pipecolinic acids.
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