Diazomethane phosphonic acid dimethyl ester

Seyferth s diazomethane phosphonic acid dimethyl ester, which enables the aldehyde —> alkyne elongation shown in Figure 14.30, is unstable. This is why Bestmann replaced it by a less sensitive synthetic equivalent, namely diazo acetone phosphonic acid dimethyl ester (Formula C in Figure 14.31), since with potassium methoxide—which is proportionately present in a solution/suspension of solid potassium carbonate in dry methanol—the dia-... 

New developments in the synthesis of a-hydroxy phosphonic acids and their derivatives have concentrated on their asymmetric formation. The chiral phosphonic diamides (629) (in which R = isopropyl, 2,2-dimethylpropyl, or benzyl or a derivative thereof) in either racemic or optically active forms were converted into their anions and allowed to react with aldehydes to give the products (630) the diastereoisomeric composition of the latter could be ascertained by the use of P NMR spectroscopy, and after acidic hydrolysis and subsequent methylation (diazomethane) it was possible to isolate optically active forms of the dimethyl esters of (l-hydroxyalkyl)phos-phonic acids, the (/ ,R)-diamide giving rise to the (5)-acids as their esters. The best results were achieved when R = Bu CFl2, and enantiomeric excesses were generally above 85% . 

Further studies on 1,3-dipolar addition reactions of diazophosphonates have been recorded,122 and work on 2-diazo-l-hydroxyalkylphosphonates also continues.123 The ester (155 R = H) reacts with esters of acetylenedicarboxylic acid without liberation of nitrogen to give stereoisomeric C-phosphorylated pyrazolines, which can be decomposed with both phosphorus-carbon and carbon-carbon bond fission, affording mixtures containing dimethyl acetylphosphonate, dimethyl hydrogen phosphonate, and tri(alkoxycarbonyl)pyrazolines. In the reaction between the same diazophosphonate and diazomethane, the latter conceivably acts as a basic catalyst for proton transfer in a series of steps which includes phosphonate-phosphate isomerization. The importance of a labile proton is demonstrated by the fact that the ester (155 R = Me) does not react in the manner described above. 

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