Organophosphorus Compounds. Part 151: Synthesis and Reactivity of a Novel Isophosphinoline Derivative

Regiospecific 1,3-dipolar cycloadditions of the carbonyl ylide 2, generated thermally from the oxirane 1, to the phosphaalkynes 3 furnish the polycyclic phosphaalkenes 4. The reaction of 4a with sulfur or gray selenium leads to the thia- or selenaphosphirane derivatives 5. An oxidation of the phosphorus atom in 5a can be achieved by the addition of a stoichiometric amount of sulfur and affords the thioxothiaphosphirane derivative 6. Thermolysis of the phosphaalkenes 4a–c gives an unexpected result: rearrangement of the ring skeleton with cleavage of the alkyl substituent at the P/C double bond to afford the isophospholine system 7 occurs. The constitution of compound 7 was deduced from its spectral data and confirmed by reactivity studies.