DETERMINATION OF THE NUCLEOPHILICITIES OF SILYL AND ALKYL ENOL ETHERS

The kinetics of the reactions of benzhydryl cations with 19 silyl enol ethers, four silyl ketene acetals, and two alkyl enol ethers have bee n determined photometrically in dichloromethane solution. All reaction s reported in this investigation follow second-order rate laws, and th e rates are independent of the nature of the complex counterion (BF4-, F3CSO3-, or ZnCl3-) in accord with rate-determining C-C bond formatio n. The nucleophilic reactivities span over a range of 10(8) from the v inyl ethers 1a,x as the least reactive compounds (comparable to allyls ilanes) to the highly nucleophilic silyl ketene acetal 1u (comparable to enamines). Linear free enthalpy relationships are used to compare t he reactivities of these compounds with those of other aliphatic and a romatic pi-nucleophiles.