REARRANGEMENTS OF (CHLOROMETHYL)ORGANYLSILANES INDUCED BY LEWIS-ACIDS ACIDS OR BY LEWIS-BASES - REGIOSELECTIVE METHYLENATION OF ALLYLIC SYSTEMS

In order to study the scope and mechanisms of the migration of organyl groups from silicon to its adjacent methylene carbon, a series of derivatives of the type R-SiMe2-CH2-Cl were synthesized, where R is vinyl, benzyl, methallyl, phenylethynyl, aryloxy, and N-methylanilino. Attempts were then undertaken to induce such Si --> C shifts by either the Lewis acid, methylaluminum dichloride, or the Lewis base, potassium fluoride. Under Lewis acidic conditions, only the benzyl and methylallyl groups could be induced to migrate; clearly, in the case of benzyl (and probably in the case of methallyl), migration was accompanied by allylic rearrangement to produce the o-tolyl group. Under the agency of KF, all the groups investigated underwent rearrangement to produce F-SiMez-CH2-R. By a crossover experiment, it was shown that, when R = aryloxy, the rearrangement occurs intermolecularly. Experimental evidence indicates that all KF-induced migrations are probably intermolecular and all MeAlCl2-induced migrations considered here. are intramolecular. The advantages for organosilicon synthesis of utilizing so-called ''relay substitution reactions'' with the Cl-SiR2-CH2-Cl system are discussed: [GRAPHICS] With unsymmetrical allylic systems, regioselective methylenation now becomes possible, simply by inducing the Si --> C rearrangement by MeAlCl2 or by KF.