Carbene Formation or Reduction of the Diazo Functional Group? An Unexpected Solvent‐Dependent Reactivity of Cyclic Diazo Imides

Abstract

The control of the reactivity of diazo compounds is commonly achieved by the choice of a suitable catalyst, e.g. via stabilization of singlet carbenes or radical intermediates. Herein, we report on the light‐promoted reactivity of cyclic diazo imides with thiols, where the choice of solvent results in two fundamentally different reaction pathways. In dichloromethane (DCM), a carbene is formed initially and engages in a cascade C‐H functionalization/thiolation reaction to deliver indane‐fused pyrrolidines in good to excellent yields. When switching to acetonitrile solvent, the carbene pathway is shut down and an unusual reduction of the diazo compound occurs under otherwise identical reaction conditions, where the aryl thiol acts as reductant. A combined set of experimental and computational studies was carried out to obtain mechanistic understanding and to support that indane formation proceeds via the insertion of a triplet carbene, while the reduction of diazo imides proceeds via an electron transfer process.

Visible photons as ideal reagents for the activation of coloured organic compounds

“…On the other hand, in MeCN as the reaction medium, a clean reaction took place and hydrazones were formed where the thiols acted as the reductant. 274…”

Visible Light-Induced Reactions of Diazo Compounds and Their Precursors

“…Very recently, the groups of Koenigs and Chauhan observed that cyclic diazo imides 103.1 are capable of engaging in two different reaction pathways in the presence of thiols under light-induced conditions (Scheme 103). 219…”

“…Very recently, the groups of Koenigs and Chauhan observed that cyclic diazo imides 103.1 are capable of engaging in two different reaction pathways in the presence of thiols under light-induced conditions (Scheme ). In acetonitrile solvent, an unusual reduction of the diazo compound to a hydrazone 103.2 was observed, with no carbene intermediate formed (Scheme a). However, in dichloromethane, a triplet carbene is generated under 365 nm light irradiation, which then participates in a cascade cyclization/thiolation reaction, ultimately yielding indane-fused pyrrolidines 103.3 (Scheme b).…”