Transition-Metal-Free Tandem Radical Thiocyanooxygenation of Olefinic Amides: A New Route to SCN-Containing Heterocycles

Abstract

A novel transition-metal-free tandem radical thiocyanooxygenation of olefinic amides with potassium thiocyanate has been developed under mild conditions. This method allows a reliable and practical access to diverse SCN-containing heterocycles bearing a wide range of functional groups in good to excellent yields. Furthermore, this tandem reaction provides a simple method for the construction of C-O and C-S bonds in one step.

Synthesis of SCF3‐Containing Benzoxazines and Oxazolines via a Photoredox‐Catalyzed Radical Trifluoromethylthiolation‐Cyclization of Olefinic Amides

“…Based on the above experimental results and previous literature, a plausible mechanism for this photocatalytic trifluoromethylthiolation/cyclization of olefinic amides is proposed in Scheme . First, the excited state fac ‐Ir(ppy) 3 * is formed by visible‐light irradiation, which subsequently serves as a reductant to reduce N ‐trifluoromethylthiosaccharin 2 a through a single‐electron transfer (SET) process with the release of a radical species A ( .…”

“…For instance, in 2015, Guo et al. first presented a metal‐free thiocyanation of olefinic amides to synthesize benzoxazines . The Xiao group reported a visible‐light‐induced oxytrifluoromethylation for the synthesis of trifluoromethylated benzoxazines and oxazolines .…”

Regioselective Synthesis of Thiocyanate‐Containing Isoxazolines via FeIII/K2S2O8‐Mediated Radical Thiocyanation/Cyclization Cascade Reaction of β,γ‐Unsaturated Oximes

“…In these transformations, the thiocyanate anion could be easily oxidized to afford the thiocyanate radical, which was utilized to achieve the direct thiocyanation of C(sp 2 )−H bonds of heterocyclic rings –. However, to the best of our knowledge, the use of thiocyante radical in a tandem cyclization reaction remains relatively unexplored . Thus, it is still desirable to develop an efficient tandem radical thiocyanation/cyclization cascade reaction for the synthesis of diverse thiocyanate‐containing heterocycles.…”

“…On the basis of the above control experimental results and investigations, we proposed the following reaction mechanisms involving two possible pathways for this transformation (Scheme ) . In path a, intermediate A formed by ligand exchange is oxidized to generate the SCN radical . The radical then attacks the carbon–carbon double bond of β,γ‐unsaturated oximes to give the alkyl radical B .…”

“…In path a, intermediate A formed by ligand exchange is oxidized to generate the SCN radical . The radical then attacks the carbon–carbon double bond of β,γ‐unsaturated oximes to give the alkyl radical B . Afterwards, radical B is further oxidized by Fe III /K 2 S 2 O 8 to give the corresponding carbon cation C .…”