Alkynyltriazenes in Photochemical Metal-Free Doyle-Kirmse Rearrangements

Abstract

Doyle-Kirmse rearrangement reactions are widely recognized as versatile and powerful synthetic tools, promoting the simultaneous generation of C─C and C─S bonds. While notable progress has been attained, Doyle-Kirmse rearrangement reactions involving cyanocarbenes have rarely been reported owing to the limited strategies available for the preparation of cyanocarbene precursors and its inherently restricted reactivity. Herein, we report photochemical Doyle-Kirmse rearrangement reactions of alkynyl triazenes via intermediate cyanocarbenes under metal- and additive-free conditions, leading to valuable α-mercapto-nitriles in generally moderate-to-good yields. In contrast to existing methods that utilize alternative cyanocarbene precurors, this approach delivers the possibility to access highly substituted stereogenic carbon centers and it offers a safer alternative by avoiding hazardous reagents. The reactions proceed under mild conditions, and demonstrate broad substrate compatibility. In addition, upscaling of the reaction was successfully demonstrated. Besides the use of allylsulfides, propargyl as well as allenylsulfides were also feasible substrates demonstrating the great synthetic potential of the transformation.

Keywords: Cyanocarbenes; Nitrile compounds; Photochemistry; Rearrangement; Triazenes.