Rhodium-catalyzed Enantioselective Synthesis and Properties of Silicon-stereogenic Benzofuranylmethylidene-benzoxasiloles

The enantioselective synthesis of silicon-stereogenic benzofuranylmethylidene-benzoxasiloles was achieved with moderate enantioselectivity by the cationic rhodium(I)/(S)-BINAP complex-catalyzed desymmetrization of symmetrical bis(2-ethynylphenol)silanes, possessing the tert-butyl and methyl groups on the silicon atom. This reaction involves 1,2-silicon/1,3-carbon migrations and oxycyclization, and the 1,2-silicon migration constructs the stereogenic silicon center. The thus obtained benzofuranylmethylidene-benzoxasiloles with the electron-donating methoxy, methyl, and phenyl groups on two benzene rings showed good fluorescence quantum yields in solution state, on the other hand, that with the electron-withdrawing trifluoromethyl groups on two benzene rings showed good fluorescence quantum yield in solid state.