Silver-promoted reaction of alkyl halide with diphenyl sulfide
In the presence of $\ce{AgBF4}$, diphenylsulfide is alkylated to 3-chloropropyl diphenylsulfonium tetrafluoroborate. The sulfonium salt is stable and can be isolated as a crystalline product.



This sufonium salt can be deprotonated (e.g. with $\ce{NaH}$ in $\ce{THF}$) to the corresponding sulfonium ylide.


In the latter, intramolecular displacement of $\ce{Cl-}$ yields cyclopropyl diphenylsulfonium tetrafluoroborate, which again is a stable solid.

This cyclopropyl derivative, once converted to its sulfonium ylide S may serve as a reagent in the Corey–Chaykovsky reaction.