ACTIVATION OF THE SILICON-HALOGEN BOND BY BISMUTH(III)HALIDES - HALOGENATION OF ALCOHOLS - PROSPECTIVE AND MECHANISM

Activation of the silicon-halogen bond by bismuth (III) halides. Halog enation of alcohols : prospective and mechanism. In the presence of ca talytic amount of BiCl3, chloromethylsilanes can be used as chlorinati ng agents for alcohols, and as chloro-dealkylating agents for silyl et hers and carboxylic and sulfonic esters. The chlorination of (R)-(-)-o ctan-2-ol and the (R)-(-)-2-mesyloctane by TMSCl gave predominantly th e (S)-(+)-2-chlorooctane with inversion of configuration at secondary carbon. According to the class of alcohol, the mechanism involves S(N) 2, S(N)2' or S(N)1 processes. This new activation of the Si-Cl bond, p robably through a Si-Cl...BiCl3 interaction gives a hard-soft reagent that can generate a silicenium cation, was also observed with Me(3)SiB r, BiBr3 and Me(3)SiI, BiI3 systems. The reaction is also presented as a possible alcoholysis of chlorosilanes, which can lead to siloxanes in non-aqueous conditions.