Generation of dialkyl phosphonodithioyl radicals and their addition onto alkenes. Synthesis of 3-phosphonodithiomethyl-3-deoxofuranosides

An efficient, three-step preparation of the new 2-phenylselanyl-[1,2,3]-dithiaphosphinane-2-oxide (8) from PCl3 is described. The reagent is shown to behave as a precursor of the corresponding phosphonodithioyl radical, when placed in the presence of tin or silyl radicals. A novel synthesis of S,S-dialkyl phosphonodithioates is described based on these results. Application of this methodology to exocyclic 3-methylene-3-deoxofuranosides leads to the highly diastereoselective formation of 3-phosphonodithiomethyl-3-deoxofuranosides.