Enantioselective Synthesis of Spirosilabicyclohexenes by Asymmetric Dual Ring Expansion of Spirosilabicyclobutane with Alkynes

Silaspiranes have attracted particular attention due to their chiral spiro-silicon center, which serves as an ideal carbon isostere and can endow spiro-analogs with distinct properties. Distinct from previously reported cyclization or cycloaddition strategies to form 5/5-silaspiranes, we report herein the asymmetric dual ring expansion of spirosilabicyclobutanes with alkynes to synthesize axially chiral spirosilabicyclohexenes bearing a novel 6/6-silaspirane framework. DFT (density functional theory) calculations provide the deep insight into the origin of the high enantioselectivity controlled by the sterically demanding binaphthyl phosphoramidite ligand. Preliminary studies of chiroptical properties indicate that one of the spirosilabicyclohexene analogs exhibit fluorescence emission, Cotton effects and CPL (circularly polarized luminescence) activity.

Automated summary

Silaspiranes with chiral spiro-silicon center have unique properties. This study reports a novel method to synthesize axially chiral spirosilabicyclohexenes with a 6/6-silaspirane framework through the reaction of alkynes with spirosilabicyclobutanes. The origin of high enantioselectivity is revealed by DFT calculations. Preliminary studies show that one of the spirosilabicyclohexene analogs exhibits fluorescence emission, Cotton effects, and CPL activity.