Synthesis of Thioethers by InI₃-Catalyzed Substitution of Siloxy Group Using Thiosilanes

The substitution of a siloxy group using thiosilanes smoothly occurred in the presence of InI₃ catalyst to yield the corresponding thioethers. InI₃ was a specifically effective catalyst in this reaction system, while other typical Lewis acids such as BF₃⋅OEt₂, AlCl₃, and TiCl₄ were ineffective. Various silyl ethers such as primary alkyl, secondary alkyl, tertiary alkyl, allylic, benzylic, and propargylic types were applicable. In addition, bulky OSitBuMe₂ and OSiiPr₃ groups, other than the OSiMe₃ group, were successfully substituted. The substitution reaction of enantiopure secondary benzylic silyl ether yielded the corresponding racemic thioether product, which suggested that the reaction of tertiary alkyl, secondary alkyl, benzylic, and propargylic silyl ethers would proceed via a S_N1 mechanism.