The photolytic reaction of thiols with diphenylvinylphosphine

Abstract

The thiols RSH react with diphenylvinylphosphine under u.v. irradiation to give Ph₂ PC₂H₄SR when R is Et, Prⁿ, Buⁿ, Ph, or C₆ F₅. If R is Bu^t or PhCH₂, however, Ph₂(vinyl)PS and RH are formed instead. The bahaviour of PrⁱSH is intermediate, and it produces Ph₂PC₂H₄ Sprⁱ, Ph₂(vinyl)PS, and Ph₂P(S)C₂H₄SPrⁱ. Excess of thiol leads to ph₂P(S)C₂H₄SR in every case. The formation of the different products can be accounted for by RS˙ radical attack on either olefin or phosphorus. The favoured route appears not to depend on the nature of RS˙, however, but on the ease of elimination of R˙, a step involved in the route to the phosphorus(V) sulphide. This mechanism demands either that RS˙ attack on P^III is readily reversible, or that the intermediate [Ph₂(vinyl)PSR]˙ readily undergoes intramolecular rearrangement. An equilibrium between the intermediates Ph₂(vinyl) P˙SR and Ph₂PC˙HCH₂SR is probably established.