Enantioselective Sulfonium-Claisen Rearrangement with Cinnamyl Thioethers

Abstract

Sulfonium-Claisen rearrangement leveraged by the gold-catalyzed formation of allyl sulfonium intermediates has enabled an exceptional level of regio- and enantiocontrol for the synthesis of skipped 1,4-dienes. However, the application of cinnamyl thioether derivatives to the sulfonium-Claisen rearrangement has been unsuccessful so far due to the extensive dissociation of the cinnamyl cation. By fine-tuning bisphosphine ligands, we were able to engage cinnamyl thioethers in the [3,3]-sigmatropic rearrangement, delivering the desired 1,4-dienes in a highly enantioselective manner and in good yields. The resulting products could be transformed into optically active 2-chromanones and 4H-chromenes having a vinyl moiety.