Acylation of diethyl (ethoxycarbonylfuryl)methanephosphonates under the conditions of claisen reaction

O,O-Diethyl (ethoxycarbonylfuryl)methanephosphonates are formylated with ethyl formate in the presence of sodium foil at the methylene group adjacent to phosphorus atom to form sodium salts of phosphonoacetic aldehyde. When the substituents in the furan ring are remote from one another, and also in the case of 3, 4-disubstituted isomer these salts in DMSO solution exist in the carbanion form. Anions of salts of (2-ethoxycarbonylfur-3-yl)phosphonoacetic aldehyde and the isomer with the reversed location of substituents in DMSO solution take part in the dynamic equilibrium between the carbanion and the enolate form. The alkylation of all salts obtained with allyl bromide and dimethyl sulfate proceeds exclusively at the oxygen to form a mixture of Z- and E-isomers of phosphorylated vinyl ethers.