"Halophilic Activation" of Chlorosilanes: Allylation of Aldehydes Catalyzed by Platinum Dichloride or Silver Triflate

PtCl2, AgOTf or Hg(CF3CO2)2 (1 - 5 mol%) efficiently catalyze the addition of allyldimethylchlorosilane to aldehydes. The reaction is highly aldehyde selective, leaving ketones, esters, nitriles, alkenes, aryl halides, ethers and nitro groups untouched. If substituted allylchlorosilanes are used, the resulting homoallyl alcohols are obtained with good to excellent diastereoselectivity. The syn : anti ratio of the products reflects the (E,Z)-ratio of the allylsilane used, thus indicating a chairlike cyclic transition state. A mechanistic rationale for the observed results is presented which implies that the chloride function of the donor is the prime site of interaction with the catalyst