Enol-keto tautomerism of alpha-ketophosphonates.

A number of alpha-ketophosphonates have been prepared and their enol-keto tautomerism has been studied by means of proton and phosphorus NMR and infrared spectroscopy and the ferric chloride test. Aliphatic ketophosphonates exist largely in the keto tautomeric forms, with only a small amount of enol forms present. All the aromatic acylphosphonates studied, however, enolize extensively. An x-ray analysis confirmed enolization and E configuration as the only stereochemical isomer. Reaction of diazomethane with diethyl p-methoxyphenylacetyl phosphonate gave a mixture of O-methylation and carbene insertion products, whereas the same reaction with diethyl isobutyryl phosphonate gave only carbene insertion products.