Direct chlorination of alcohols with chlorodimethylsilane catalyzed by a gallium trichloride/tartrate system under neutral conditions

Abstract

The reaction of secondary alcohols 1 with chlorodimethylsilane (HSiMe₂Cl) proceeded in the presence of a catalytic amount of GaCl₃/diethyl tartrate to give the corresponding organic chlorides 3. In the catalytic cycle, the reaction of diethyl tartrate 4a with HSiMe₂Cl 2 gives the chlorosilyl ether 5 with generation of H₂. Alcohol-exchange between the formed chlorosilyl ether 5 and the substrate alcohol 1 affords alkoxychlorosilane 6, which reacts with catalytic GaCl₃ to give the chlorinated product 3. The moderate Lewis acidity of GaCl₃ facilitates chlorination. Strong Lewis acids did not give product due to excessive affinity for the oxy-functionalities. Although tertiary alcohols were chlorinated by this system even in the absence of diethyl tartrate, certain alcohols that are less likely to give carbocationic species were effectively chlorinated using the GaCl₃/diethyl tartrate system.