STEREOCHEMISTRY OF THE REACTION OF α,α-DIBROMOKETONES WITH ETHYL DIPHENYLPHOSPHINITE. MOLECULAR STRUCTURE OF O-(1-PHENYL-2-BROMOVINYL)DIPHENYLPHOSPHINATE

Abstract

The reaction of α,α-dibromoacetophenone (1) with ethyl diphenylphosphinite (2) gives solid O-(Iphenyl-2-bromovinyl)diphenylphosphin ate (3) as one stereoisomeric product. The stereochemistry of 3 is shown to be the Z configuration by single crystal X-ray analysis. A Z configuration for 3 had been predicted based on the postulated mechanism for its formation featuring nucleophilic attack on bromine by the phosphinite to give an enolate phosphonium ion-pair which then interacts further. Several lines of evidence link this demonstrated stereochemistry for 3 with a Z configuration for the major stereo-isomeric enol phosphate formed in the Perkow reaction of several α-haloketones with trialkyl phosphites. Z Configurations for two different crystalline enol phosphates have been demonstrated via X-ray analysis by Zwierzak and by Rohrbaugh and Jacobson, respectively.

Key Words:

• Stereochemistry
• Perkow reaction
• enol phosphinate
• bromophilic attack.