Deoxygenation of chalcogen oxides EO2 (E = S, Se) with phosphaWittig reagents

In here we present the deoxygenation of chalcogen oxides EO2 (E = S, Se) with phosphanylidene-σ4-phosphoranes, also referred to as phospha-Wittig reagents. The reaction of DABSO (DABCO⋅2SO2) with R–P(PMe3) (R = Mes*, 2,4,6-tBu3-C6H2; MesTer, 2,6-(2,4,6-Me3-C6H2)2-C6H3) resulted in the formation of three-membered thiadiphosphiranes (RP)2S (1:R). In similar fashion the reaction with SeO2 afforded selenadiphosphiranes (RP)2Se (2:R). Utilizing the sterically more encumbered DipTer– P(PMe3) (DipTer = 2,6-(2,6-iPr2-C6H3)2-C6H3) less selective reactions were observed. Here, reaction with DABSO (or with equimolar ratios of SeO2 at elevated temperatures) gave rise to the formation of the PMe3O-stabilized dioxophosphorane (phosphinidene dioxide) DipTerP(O)2–OPMe3 (3:DipTer) as the main product. Mass spectrometric investigations furthermore indicate the formation of a series of asymmetric dimers of chalcogenaphosphoranes DipTerPE1 and dichalcogenaphosphoranes DipTerP(E1E2)2 (E1,2 = O, S) of the general formula (DipTerP)2S3–xOx (x = 0, 1, 2) when using DABSO. By2 carefully screening the reaction conditions of DipTer−P(PMe3) with SeO2 the selenadiphosphirane (DipTerP)2Se (2:DipTer) and the four-membered ring species (DipTerPSe)2 (8:DipTer) were obtained. Thus, phospha-Wittig reagents are useful synthetic tools for the metal-free deoxygenation of EO2 (E = S, Se).