Enantioselective Synthesis of 6/5-Spirosilafluorenes by Asymmetric Ring Expansion of 4/5-Spirosilafluorenes with Alkynes.

A rhodium-catalyzed asymmetric ring expansion of 4/5-spirosilafluorenes with terminal alkynes has been developed using sterically demanding binaphthyl phosphoramidite ligand. The reaction is not only strategically distinct from cyclization or cycloaddition but also showcases the first enantioselective synthesis of axially chiral 6/5-spirosilafluorenes.