RADICAL ADDITION TO THE CARBONYL CARBON OF KETONES PROMOTED BY AQUEOS TITANIUM TRICHLORIDE IN ACIDIC MEDIUM. ONE STEP SYNTHESIS OF PINACOLS AND LACTONES.

Article abstract of DOI:10.1016/S0040-4020(01)87455-X

Carbon centered radical 1, generated by reduction of methyl phenylglyoxalate with Ti(III) ion, adds to the carbonyl carbon of ketones 2 to afford pinacols 3.Yields of 3 are remarkably influenced by the structure of 2, in that the reaction is very sensitive to steric factors.Many other functional groups present in 2 do not interfere with carbonyl addition, but lactonization of 3 occurs when the additional groups are COOH, COOC2H5, and OH.Alkyl radical addition to ketones is a reversible process, but the rapid reduction of the resulting alkoxy radical 8 by Ti(III) ion makes the whole process practically irreversible and accounts for pinacol formation.