No abstract

Through the incorporation of a silicon atom to an aryl carboxylic ester substrate, the resulting C-Si bond can be activated via the addition of a carbene catalyst on a remote site. This strategy allows for efficient functionalization of the benzylic sp-carbons of aryl carboxylic esters.

A carbene-catalyzed sulfonylation reaction between enone aryl aldehydes and sulfonyl chlorides is disclosed. The reaction effectively installs sulfone moieties in a highly enantioselective manner to afford sulfone-containing bicyclic lactones. The sulfonyl chloride behaves both as an oxidant and a nucleophilic substrate (via its reduced form) in this N-heterocyclic carbene (NHC)-catalyzed process. The NHC catalyst provides both activation and stereoselectivity control on a very remote site of enone aryl aldehyde substrates. Water plays an important role in modulating catalyst deactivation and reactivation routes that involve reactions between NHC and sulfonyl chloride. Experimental studies and DFT calculations suggest that an unprecedented intermediate and a new oxidation mode of the NHC-derived Breslow intermediate are involved in the new asymmetric sulfonylation reaction.

An N‐heterocyclic carbene (NHC)‐catalyzed reaction between α‐bromoenals and 2‐aminoaldehydes has been developed. Key steps include chemoselective reaction of the NHC catalyst with one of the aldehyde substrates (the bromoenal) to eventually generate an α,β‐unsaturated acylazolium intermediate. Addition of the nitrogen atom of aminoaldehyde to the unsaturated azolium ester intermediate followed by intramolecular aldol reaction, β‐lactone formation, and decarboxylation leads to chiral dihydroquinolines with high optical purity. The dihydroquinoline products, which are quickly prepared by using this method, can be readily transformed into a diverse set of functional molecules such as pyridines and chiral piperidines.

Disclosed here is a catalytic strategy for asymmetric access to chiral tetrasubstituted silicon-stereogenic silanes. Our reaction starts with a (covalently) symmetric silane bearing two aldehyde moieties as the substrate. Single-crystal structural analysis shows that the substrate exists as a racemate of two conformational enantiomers because of the presence of a Si/O weak interaction. Mechanistic studies assisted by DFT calculation indicate that the two conformational enantiomers can readily isomerize to each other, and one of the conformational enantiomers of the substrate is favorably activated by a N-heterocyclic carbene catalyst via an overall desymmetrization process to eventually afford optically enriched tetrasubstituted silicon-stereogenic silanes as the products. Our chiral silanes’ products can be readily transformed to a diverse set of silicon stereogenic functional molecules.