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 19a and 19b and to selenophosphorodithioates 21a and 21b. Interaction of these substrates with Lawesson's reagent yields the corresponding selenophosphorothioates 20a and 20b and the selenophosphorotrithioates 22a and 22b. 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 19b 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-exo-methylene derivative 37 to diastereoselectively furnish five new 3-phosphonomethyl-, 3-phosphonothiomethyl-, and 3-phosphonodithiomethyl-3-deoxofuranoses 38a−c and 38f,g. The possibility of conducting tandem processes is also discussed through experiments involving (1R)-(+)-α-pinene (39) and diallylamine 41.将苄基亚磷酸二烷基酯与二硫代亚磷酸酯用苯硒基氯处理，可发生类阿尔布佐夫（Arbuzov）反应，生成硒代磷酸二烷基酯19a、19b与二硫代硒代磷酸酯21a、21b。将上述底物与劳森试剂（Lawesson's reagent）反应，可得到对应的硫代硒代磷酸酯20a、20b与三硫代硒代磷酸酯22a、22b。当在氢给体与烯烃共存的条件下用自由基引发剂处理时，全部8种五价磷前驱体均会发生P−Se键的均裂，生成膦酰基、硫代膦酰基、二硫代膦酰基及三硫代膦酰基自由基。研究表明，其中多数自由基可与富电子及缺电子烯烃发生加成反应，以中等至优异的收率得到目标加成产物。环状前驱体19b则表现出特殊的反应行为，仅能在该反应条件下生成对应的环状亚磷酸酯。将该自由基链式反应应用于呋喃糖基3-外向亚甲基衍生物37，可通过非对映选择性路径得到5种全新的3-膦酰甲基、3-硫代膦酰甲基及3-二硫代膦酰甲基取代的3-脱氧呋喃糖38a~c、38f、g。本研究还通过以(1R)-(+)-α-蒎烯(39)与二烯丙基胺(41)为底物的实验，探讨了开展串联反应的可行性。