Deoxygenation of chalcogen oxides EO (E = S, Se) with phospha-Wittig reagents.

In here we present the deoxygenation of the chalcogen oxides EO (E = S, Se) with R-P(PMe), so-called phospha-Wittig reagents. The reaction of DABSO (DABCO·2SO) with R-P(PMe) (R = Mes*, 2,4,6-Bu-CH; Ter, 2,6-(2,4,6-Me-CH)-CH) resulted in the formation of thiadiphosphiranes (RP)S (1:R), while selenadiphosphiranes (RP)Se (2:R) were afforded with SeO, both accompanied by the formation of OPMe. Utilizing the sterically more encumbered Ter-P(PMe) (Ter = 2,6-(2,6-iPr-CH)-CH) a different selectivity was observed and (TerP)Se (2:DipTer) along with [Se(μ-PTer)] (3:DipTer) were isolated as the Se-containing species in the reaction with SeO. Interestingly, the reaction with DABSO (or with equimolar ratios of SeO at elevated temperatures) gave rise to the formation of the OPMe-stabilized dioxophosphorane (phosphinidene dioxide) TerP(O)-OPMe (4:DipTer) as the main product. This contrasting reactivity can be rationalized by two potential pathways in the reaction with EO: (i) a Wittig-type pathway and (ii) a pathway involving oxygenation of the phospha-Wittig reagents and release of SO. Thus, phospha-Wittig reagents are shown to be useful synthetic tools for the metal-free deoxygenation of EO (E = S, Se).