Dialkyl arylcarbonylphosphonates in the reactions with 2-RO-4-oxo-5,6-benzo-1,3,2-dioxaphosphorinanes. Steric structure of the derivatives of 4-aryl-2-hydroxy-4-dialkoxyphosphoryl-5-oxo-6,7-benzo-1,3,2-dioxaphosphepine 2-oxides

2-RO-4-Oxo-5,6-benzo-1,3,2-dioxaphosphorinanes react with dialkyl arylcarbo nylphosphonates with high regioselectivity and moderate stereoselectivity t o form 2-R-5-oxo-4-aryl-4-dialkoxyphosphoryl-6,7-benzo-1,3,2-dioxaphosphepi ne 2-oxides whose structure was confirmed by NMR and IR spectroscopy. Selec tive hydrolysis of 2-alkoxy-6,7-benzo-1,3,2-dioxaphosphepines results in el imination of the exocyclic alkoxy group, and partially esterified phosphori c acids are formed. The structure of the acids giving the crystal hydrates was established by X-ray diffraction.