Stereoselective Addition of Alcohols to Stable Disilenes

1,2-Addition of methanol, ethanol and 2-propanol in C 6 D 6 to E-1,2-di-terf-butyl-1,2-dimesityldisilene (E-1), or 1,2-di-ferf-butyl-1,2-bis(2,4,6-tri/'so-propylphenyl)disilene (E-2), and of methanol and ethanol to Z-1,2-di-tert-butyl-1,2-bis(2,4,6-tri/'sopropylphenyl)disilene (Z-2), take place across the Si=Si double bond with high syn stereoselectivity. Lower stereoselectivity was found for ethanol addition to E-1 in THF. The results are explained in terms of a pathway involving a zwitterionic intermediate.