Phosphonyl, Phosphonothioyl, Phosphonodithioyl, and Phosphonotrithioyl Radicals:  Generation and Study of Their Addition onto Alkenes^†

The treatment of benzyl dialkyl phosphites and dithiophosphites with benzeneselanyl chloride generates an Arbuzov-type transformation leading to the dialkyl selenophosphates <b>19a</b> and <b>19b</b> and to selenophosphorodithioates <b>21a</b> and <b>21b</b>. Interaction of these substrates with Lawesson's reagent yields the corresponding selenophosphorothioates <b>20a</b> and <b>20b</b> and the selenophosphorotrithioates <b>22a</b> and <b>22b</b>. When treated with a radical initiator in the presence of a hydrogen donor and an alkene, all eight phosphorus(V) precursors undergo homolytic cleavage of the P−Se bond to generate the phosphonyl, phosphonothioyl, phosphonodithioyl, or phosphonotrithioyl radicals. Most of these are shown to add onto electron-rich and electron-poor alkenes to deliver the expected adducts in fair to excellent yields. Cyclic precursor <b>19b</b> displays peculiar behavior and, under the reaction conditions, produces only the corresponding cyclic phosphite. Application of this radical chain process is carried out on furanosyl 3-<i>exo</i>-methylene derivative <b>37</b> to diastereoselectively furnish five new 3-phosphonomethyl-, 3-phosphonothiomethyl-, and 3-phosphonodithiomethyl-3-deoxofuranoses <b>38a</b>−<b>c</b> and <b>38f</b>,<b>g</b>. The possibility of conducting tandem processes is also discussed through experiments involving (1<i>R</i>)-(+)-α-pinene (<b>39</b>) and diallylamine <b>41</b>.