One-step synthesis of fluorenyl-substituted chlorosilanes: Friedel-Crafts type cycloalkylation of biphenyl with (dichloroalkyl)silane

Abstract

Friedel-Crafts alkylation reactions of biphenyl with (dichloroalkyl)chlorosilanes [Cl3-mMemSi-(CnH2n-1Cl2), m = 0-2, n = 1-3] at temperatures ranging from 120 to 160 degreesC in the presence of a Lewis acid catalyst gave cyclized products, fluorenyl-substituted chlorosilanes, in 47-94% yields. In these reactions, the reactivities of (dichloroalkyl)silanes generally increase as the number of methyl groups on the silicon atom and the alkyl chain length increase. However, desilylation of the alkylated products and starting chlorosilanes was observed in the case of (dichloroalkyl)silanes having two or more methyl groups on the silicon. Alkylation with (dichloromethyl)dimethylchlorosilane proceeded at 120 degreesC but gave fluorene and dimethyldichlorosilane resulting from desilylation of the products. The reactivities of (dichloroalkyl)silanes decrease in the following order: m = 2 > 1 > 0; n = 2 > 1. The catalytic efficiencies of Lewis acids for the cycloalkylation reactions decrease in the following order: AlCl3 > AlBr3 > HfCl4 > ZrCl4 much greater than TiCl4.