Access to axially chiral styrenes via a photoinduced asymmetric radical reaction involving a sulfur dioxide insertion

Abstract

The wide applicability in various fields enables development of novel methods to access axially chiral styrenes to be of significance. Among the developed and potential synthetic strategies for this type of framework, the route based on an asymmetric radical process is more challenging and has not been achieved so far. Here we report a photo-promoted, three-component, asymmetric free radical reaction of potassium alkyltrifluoroborates, potassium metabisulfite, and 1-alkynylnaphthalen-2-ols, delivering axially chiral ( S , E )-1-(1-(alkylsulfonyl)-2-vinyl)naphthalen-2-ols with excellent enantioselectivity (93%–99% enantiomeric excess) and good yield (up to 97%). The transformation involves in situ generation of alkylsulfonyl radicals, tandem enantioselective radical addition, and a reduction process of radical species. • Photoinduced asymmetric catalytic radical approach to access axially chiral styrenes • A rare success in the field of asymmetric sulfur dioxide insertion • Broad substrate scope with excellent enantioselectivity and regioselectivity Development of new pathways for generation of axially chiral styrenes has gained great attention in recent years because of the wide applicability of axially chiral styrenes in chiral ligands, catalysts, and functional materials. Among the developed and potential synthetic strategies for synthesis of axially chiral styrenes, the synthetic route through an asymmetric radical process is more challenging and has not been achieved so far. Here we developed a photoinduced asymmetric catalytic radical approach to access sulfonyl-containing axially chiral styrenes with excellent enantioselectivity, regioselectivity, good yield, and broad substrate scope. Control experiments and DFT calculations were carried to understand the mechanism and the origin of the high enantioselectivity and Z/E selectivity of the reaction. Photoinduced three-component asymmetric free radical reaction of potassium alkyltrifluoroborates, potassium metabisulfite and 1-alkynylnaphthalen-2-ols, delivering axially chiral ( S , E )-1-(1-(alkylsulfonyl)-2-vinyl)naphthalen-2-ols with excellent enantioselectivity (93%–99% ee) and good yield (up to 97%). The transformation involves in situ generation of alkylsulfonyl radicals and a tandem enantioselective radical addition process.