Organophosphorus compounds; 142: A simple approach to 1,2,4-selena- and telluradiphospholes from phosphaalkynes and the chalcogen elements and a first study of their reactivity

Phosphaalkynes 3 react with elemental selenium or tellurium to furnish the 1,2,4-selena- (5) or 1,2,4-tellutadiphospholes (15), respectively. Although the telluradiphuspholes 15 do not exhibit any selective cycloaddition reac tivity, two equivalents of the phosphaalkyne 3 do undergo cycloaddition to the selenadiphospholes 5 through a [4+2]/[2+2+2] sequence to afford the tet racyclic products 8. The crystal structure of compound 80 has been determin ed, This cage compound is alkylated at P-4 on reaction with methyl trifluor omethanesulfonate to give 10 while selenium and sulfur react at P-7 of 8 to afford 11a,b. Compound 80 reacts with bromine by way of P/P bond cleavage and an unexpected rearrangement to furnish another tetracyclic compound 12 with a novel structure that has been confirmed by X-ray crystallography.