Development of new synthetic strategies for enantioselective carbon-carbon and carbon-heteroatom bond formation is one of the pillars of modern organic chemistry. Whereas significant advances have been achieved in center chirality construction, catalytically asymmetric construction of axial chirality is still under development. Moreover, axially chiral molecules constructed through carboncarbon and carbon-heteroatom bond cleavage are extremely limited. Here, we report an asymmetric synthesis of biaryl atropisomers via palladium-catalyzed chemoselective carbon-carbon cleavage of 9-aryl-9H-fluoren-9-ols. The reaction demonstrated broad substrate scope and produced the atropisomers in high yields and enantioselectivity. The ring-opening reactivity was considerably accelerated by the torsional strain created by the steric repulsion between two ortho-substituents of the biaryl skeleton in the substrates. The high enantiocontrol hinges on the evolvement of a new TADDOL-based phosphoramidite as ligand. These findings set up a new platform for the development of novel synthetic methods via asymmetric carbon-carbon cleavage.
A hydroacylation reaction of alkenes has been achieved employing readily available carboxylic acids as the acyl source and hydrosilanes as a hydrogen source via photoredox catalysis. The combination of both single electron transfer and hydrogen atom transfer steps has dramatically expanded new applications of carboxylic acids in organic synthesis. The protocol also features extremely mild conditions, broad substrate scope, and good functional group tolerance, affording a novel and convenient approach to hydroacylation of alkenes.
Domino-fluorination-protodefluorination decarboxylative cross-coupling of α-keto acids with styrene has been developed via photoredox catalysis. The critical part of this strategy is the formation of the carbon-fluorine (C-F) bond by the capture of a carbon-centered radical intermediate, which will overcome side reactions during the styrene radical functionalization process. Experimental studies have provided evidence indicating a domino-fluorination-protodefluorination pathway with α-keto acid initiating the photoredox cycle. The present catalytic protocol also affords a novel approach for the construction of α,β-unsaturated ketones under mild conditions.
The present work demonstrates a palladium-catalyzed kinetic resolution/ring-opening reaction of 8H-indeno[1,2c]thiophen-8-ols. The reaction proceeds in a highly regioselective manner, and both optically active thiophene-phenyl atropisomers and stereogenic 8H-indeno[1,2-c]thiophen-8-ols were obtained with high enantiomeric excesses. The synthetic applications of the obtained thiophenyl atropisomers were briefly investigated.
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