Reaction of 2-R-4-oxo-5,6-benzo-1,3,2-dioxaphosphorinanes with Methyl 2-oxo-3,3,3-trifluoropropionate. Steric Structure of 5-oxo-4-methoxycarbonyl-4-trifluoromethyl-2-ethoxy-6,7-benzo-1,4,2-dioxaphosphepine 2-oxide

Reaction of 2-R-4-oxo-5,6-benzo-1,3,2-dioxaphosphorinanes with methyl 2-oxo -3,3,3-trifluoropropionate, depending on the order of mixing the reactants and on temperature, yields either the products of ring extension, 5-oxo-4-m ethoxycarbonyl-4-trifluoromethyl-2-ethoxy-6,7-benzo-1,4,2-dioxaphosphepine 2-oxides, with a high regioselectivity, or pentaalkoxyspirophosphoranes wit h a moderate stereoselectivity. The structure of the products was determine d by H-1, C-13, F-19, and P-31 NMR spectroscopy. The steric structure of th e isolated diastereomer of 5-oxo-4-methoxycarbonyl-4-fluoromethyl-2-ethoxy- 6,7-benzo-1,4,2-dioxaphosphepine 2-oxide was studied by single crystal X-ra y diffraction.