Medium-sized heterocycles: Synthesis of a 2,10-Bis(alkoxycarbonyl)-substituted 6-Oxo-12H-dibenzo[d,g][1,3,2]dioxaphosphocin

The synthesis and characterization of a 2,10-bis(alkoxycarbonyl)-substituted 6-oxo-12H-dibenzod,g]1,3,2]-dioxaphosphocin, 6 , is described. The lack of an observable ⁵J_HP coupling of phosphorus to the downfield C-12 methylene proton and the observation of a ²J_HCH geminal coupling constant of 14 Hz suggest that the conformation of 6 in solution is not solely a boat-chair conformation, but may involve a rapid equilibrium of the boat-chair with either a boat or twist-boat conformation.