Synthesis and structural characterization of isomeric coumarino-1,2-oxaphosphole derivatives

The coumarino-[3,4-c]-3H-10-methyl-2-oxo-2-phenyl-1,2-oxaphosphole was prepared by the addition of PhPCl2 to 3-acetylcoumarin in the presence of acetic anhydride. Its conversion to the isomeric coumarino-[3,4-c]-9H-9-methyl-2-oxo-2-phenyl-1,2-oxaphosphole was studied in different reaction conditions. The structures of the two isomers were determined by X-ray crystallography and by ab initio molecular orbital calculations.