DIRECT AND REGIOCONTROLLED SYNTHESIS OF ALPHA-PHENYL KETONES FROM SILYL ENOL ETHERS AND DIPHENYLIODONIUM FLUORIDE

The efficacy of diphenyliodonium fluoride (1, DIF) for the phenylation of silyl enol ethers was investigated. When the silyl enol ethers of cyclopentanone, 2-methylcyclopentanone, cyclohexanone, 2-methylcyclohexanone, acetophenone, 2-pentanone, diisopropyl ketone, and pinacolone were mixed with DIF in tetrahydrofuran, either alpha-phenyl or alpha,alpha-diphenyl ketones were produced and isolated in yields ranging from 20 to 88%. That the regiochemistry of alpha-phenylation can be controlled by an appropriate choice of silyl enol ether was demonstrated with the kinetic and thermodynamic silyl enol ethers of 2-methylcyclohexanone, the thermodynamic silyl enol ether of 2-methylcyclopentanone, and the kinetic silyl enol ether of 2-pentanone. 3,3-Dimethyl-2-(silyloxy)-1-butene gave a dehydro dimer of pinacolone with DIF in addition to alpha-phenylpinacolone, thus suggesting that phenylations of silyl enol ethers with DIF may proceed via radical intermediates.