REACTIONS OF DIPHENYLPHOSPHINE WITH ALPHA-SUBSTITUTED KETONES . A NEW DEHALOGENATION AND DEMESYLATION PROCEDURE

Diphenylphosphine converts acyclic α-halo ketones and α-mesyloxyketones into the dehalogenated or demesylated ketone, respectively. Reaction with cyclohexanone, α-chlorocyclohexanone, or α-mesyloxycyclohexanone gives the corresponding carbonyl adduct, an α-hydroxydiphenylphosphine, which is isolated as the phosphine oxide. The debromination reaction exhibits a moderate and negative Hammett ρ value. The reaction of diphenylphosphine with α-bromoacetophenone or with 2,4,6-trimethyl-α-bromoacetophenone, a hindered carbonyl case, proceeds at about the same rate. These facts, as well as other data which are given, suggest that the dehalogenation reactions proceed via nucleophilic displacement on halogen by phosphorus with transfer of an incipient proton to carbonyl oxygen. Other mechanistic pathways and the scope of the reactions of carbonyl compounds with diphenylphosphine are discussed. © 1969, American Chemical Society. All rights reserved.