Wittig-Horner reaction Diethyl phosphonate

The MBH reactions of diethyl vinylphosphonate dates back to 1990, and they present similar reactivities to alkyl acrylates. It was found that diethyl vinylphosphonate can be coupled with various aliphatic aldehydes in the presence of DABCO to give moderate to high yields of the corresponding a-hydroxyalkyl phosphonates 85. However, this approach was not effective for aqueous formaldehyde and polyoxymethylene, and the corresponding a-hydroxymethyl phosphonates 87 can only be obtained through a Wittig Horner-type reaction from tetraethyl methylenediphosphonate 86 and formaldehyde (30% aq.) in the presence of a weak base K2CO3 (6-8 m) (Scheme 1.42). 

When the halogen compound employed in the first step has an activated halogen atom (RCH CHCHjX, QHjCHjX, XCH2CO2H) a simpler procedure known as the Horner phosphonate modification of the Wittig reaction is applicable. When benzyl chloride is heated with triethyl phosphite, ethyl chloride is eliminated from the initially formed phosphonium chloride with the production of diethyl benzylphosphonate. This phospho-... 

Earlier it was shown that by the use of cyclic phosphonates it is possible to modify the steric course of the Horner-Emmons-Wittig reaction. Treatment of diethyl ben-zoylphosphonate with an acyclic and a five-membered cyclic phosphonate led to the formation of vinylphosphonates of opposite stereochemistry (equation 65). ... 

Phosphonate carbanions, formed by percolation of a dilute ether solution of the diethyl phos-phonate through a macroporous AER in HO" form, react with carbonyl compounds in Horner-Wittig syntheses of alkenes (Scheme 20). " a,j -Unsaturated nitriles are formed from both aldehydes and ketones, but a,) -unsaturated esters are formed only from aldehydes. The reactions... 

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