Synthetic approaches to unsaturated five-membered heterocycles containing both ring and side-chain phosphorus atoms

The syntheses of several structurally interesting 2-diphenylphosphinyl-substituted 2-phospholenes and phospholanes are reported together with a discussion of the ₃₁P and 13° C nmr spectral properties of these compounds. Several of these syntheses were found to be highly stereoselective and the potential of some of the products of these reactions as precursors to phosphole derivatives bearing phosphorus-containing side-chains has also been explored. A new, and possibly general, route to 4-oxo-2-phospholene oxides or sulfides from the corresponding 4-methylene compounds is also reported. This route involves an unusual free-radical catalyzed oxidative cleavage of the 4-methylene group by molecular oxygen and a probable mechanism for this reaction is proposed.