FRIEDEL-CRAFTS ALKYLATION OF SUBSTITUTED BENZENES BY ALLYLDICHLOROSILANE

A Friedel-Crafts type reaction of substituted benzenes with allyldichl orosilane in the presence of aluminum chloride as a catalyst resulted in alkylation, giving 3-aryl-1,1-dichloro-1-silabutanes in good yields (60-85%). All the isomeric products derived from the alkylation were identified and the relative alkylation rates of substituted benzenes w ere determined by GLC. The alkylation of substituted benzenes with all yldichlorosilane at temperatures below 0-degrees-C gave ortho- and par a-directing products at an early stage, but the products isomerized to the meta isomer as the reaction proceeded for prolonged times or at m oderately higher reaction temperature. The competitive alkylation rate s of substituted benzenes having various substituents (X) decreased in the following order: X = Ph > PhO > i-Pr > Et > Me > H > F > Cl > Br. When the alkylation rates of substituted benzenes with respect to ben zene (log k(x)/k(H)) were plotted against the substituent coefficients (sigma), a good linear relationship was observed. The results showed that electron-donating groups on the benzene ring generally facilitate the alkylation, while electron-withdrawing groups are deactivating. T his alkylation method is a good route to (2-arylpropyl)-dichlorosilane s having a Si-H functionality groups into the silanes.