The Horner-Emmons modification is a variation of a Wittig reaction in which a phosphonate-stabilized carbanion in used instead of a phosphonium ylide.

The phosphonate-stabilized carbanion is prepared from an appropriate alkyl halide. This is called the Arbuzov reaction.

Because the Arbuzov reaction can be carried out with an α-bromo ketone or an α-bromo ester (in which case it is called a Perkow reaction), it provides a way to synthesize α,β unsaturated ketones and esters.

a. Propose a mechanism for the Arbuzov reaction.
b. Propose a mechanism for the Horner-Emmons modification.
c. Show how the following compounds can be prepared from the given starting material:
1.

2.

Transcribed Image Text:

R CH CH3 CH3 Et = CH3CH2 strong base CH,C-POEt)2 (EtO)P: CH,ÇHCH3 CH3 CH3 +CH,CH2Br O strong base(EtO)2 (Eto2P-CH2 + CH3CH2Br CH,CH-CH- CH,CH-CH-CHCCH, → ОСН,