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

The reaction of secondary alcohols 1 with chlorodimethylsilane (HSiMe(2)Cl) proceeded in the presence of a catalytic amount of GaCl(3)/diethyl tartrate to give the corresponding organic chlorides 3. In the catalytic cycle, the reaction of diethyl tartrate 4a with HSiMe(2)Cl 2 gives the chlorosilyl ether 5 with generation of H(2). Alcohol-exchange between the formed chlorosilyl ether 5 and the substrate alcohol 1 affords alkoxychlorosilane 6, which reacts with catalytic GaCl(3) to give the chlorinated product 3. The moderate Lewis acidity of GaCl(3) 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 GaCl(3)/diethyl tartrate system.