A direct decarboxylative strategy for the generation of aza‐o‐quinone methides (aza‐o‐QMs) by N‐heterocyclic carbene (NHC) catalysis has been discovered and explored. This process requires no stoichiometric additives in contrast with current approaches. Aza‐o‐QMs react with trifluoromethyl ketones through a formal [4+2] manifold to access highly enantioenriched dihydrobenzoxazin‐4‐one products, which can be converted to dihydroquinolones through an interesting stereoretentive aza‐Petasis–Ferrier rearrangement sequence. Complementary dispersion‐corrected density functional theory (DFT) studies provided an accurate prediction of the reaction enantioselectivity and lend further insight to the origins of stereocontrol. Additionally, a computed potential energy surface around the major transition structure suggests a concerted asynchronous mechanism for the formal annulation.
An enantioselective cross-dehydrogenative coupling (CDC) reaction to access tetrahydropyrans has been developed. This process combines in situ Lewis acid activation of a nucleophile in concert with the oxidative formation of a transient oxocarbenium electrophile, leading to a productive and highly enantioselective CDC. These advances represent one of the first successful applications of CDC for the enantioselective couplings of unfunctionalized ethers. This system provides efficient access to valuable tetrahydropyran motifs found in many natural products and bioactive small molecules.
A chiral bicyclic bridgehead phosphoramidite (briphos) prepared from 1-aminoindane is a highly efficient and selective ligand for rhodium(I)-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated N,N-dimethyl-sulfamoyl imino esters at ambient temperature. This transformation provides a new class of chiral (Z)-γ,γ-diaryl-α,β-dehydroamino esters with excellent yield and enantioselectivity.
A rational approach for generating 1,1'-binaphthalene-like axial chirality of a small organic receptor, 2,2'-dihydroxybenzil is presented. The receptor combines with 2 equiv of monodentate primary amines to form a diimine, of which axial chirality is controlled by steric strain with moderate (1.4:1) to good (4.7:1) stereoselectivity. The observed circular dichroism (CD) spectra have been closely simulated by TD-DFT computations and can be used for determining the absolute chirality and enantiomeric excess of primary amines.
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