# Regio- and stereoselective tert-butylthiolation of internal alkynes with thioethers initiated and maintained by silylium-ion catalysis

## TL;DR

A new method for adding thioethers to internal alkynes is developed using silylium-ion catalysis, avoiding unwanted side reactions.

## Contribution

The use of silylium-ion catalysis with substoichiometric arylsilane to suppress hydrothiolation and enable selective carbothiolation is novel.

## Key findings

- A silylated sulfonium ion is catalytically formed as a tert-butyl cation source.
- Substoichiometric arylsilane suppresses β-elimination and hydrothiolation pathways.
- The method synthesizes sterically crowded aryl vinyl sulfides, sulfoxides, and sulfones.

## Abstract

A two-component protocol for the regio- and trans-selective addition of aryl tertiary alkyl (especially tert-butyl) thioethers across internal C

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C triple bonds is reported. This carbothiolation is initiated by the catalytic formation of a silylated sulfonium ion as a tertiary carbenium ion (tert-butyl cation) source. Competing loss of a proton by β-elimination of that carbenium-ion intermediate and as such a potential hydrothiolation pathway are efficiently suppressed by the substoichiometric addition of an arylsilane as a “proton-into-silylium ion” generator. Through this, the silylium-ion activation is restored, thereby maintaining the carbothiolation pathway. The method enables the synthesis of sterically crowded, fully substituted aryl vinyl sulfides as well as the sulfoxides and sulfones.

A silylium-ion-promoted carbothiolation of internal CC triple bonds is presented. Competing hydrothiolation is mitigated by the addition of substoichiometric amounts of an arylsilane as a “proton-into-silylium ion” generator.