Novel 3<i>H</i>‐1,2,3‐Dithiaphosphole and Unprecedented 1,3,2,4‐Dithiadiphosphinane Heterocycles: Unanticipated Cyclization Reactions of Lawesson's Reagent and Alkynes

The treatment of Lawesson's reagent with selected alkyl or aryl alkynes results in the formation of cyclization products such as 3 H ‐1,2,3‐dithiaphosphole‐3‐sulfide or unprecedented 1,3,2,4‐dithiadiphosphinane‐2,4‐disulfide derivatives. The new heterocycles are characterized spectroscopically and in two cases by crystal structure analyses. Density functional theory (DFT) computations (PW6B95D3/6‐311 + G(d,p)‐PCM(toluene)//B97D3/6‐31 G*) explain the formation of the dithiaphosphole product from alkynes and Lawesson's reagent via a sequence of [2 + 2] addition, electrocyclic ring opening, SS bond forming ring closure, and P(III) oxidation by sulfur transfer from Lawesson's reagent. Based on DFT calculations, the formation of a 1,3,2,4‐dithiadiphosphinane‐2,4‐disulfide is rationalized by a sequence of cyclization, electrocyclic ring opening, and dipolar cyclization steps.