Catalyst-Free Regioselective C-3 Thiocyanation of Imidazopyridines

Abstract

A direct and straightforward approach for highly regioselective thiocyanation of imidazoheterocycles through sp(2) C-H functionalization has been realized at room temperature. Various C-3 thiocyanated imidazopyridines are formed in moderate to good yield. The present method exhibits a mild and selective access to a variety of imidazopyridine derivatives of pharmacological interest.

Synthesis of Triazolium Inner Salts by Thiocyanation of Aldehyde‐Derived Hydrazones

“…On the basis of previous reports and our past experiences, we proposed a possible reaction mechanism (Scheme ). Thiocyanogen ( A ) is initially formed by oxidation of NH 4 SCN using (NH 4 ) 2 S 2 O 8 and subsequently undergoes electrophilic addition with 1a to produce cationic intermediate B . Next, the elimination of a proton from B produces thiocyanate intermediate C , which rearranges through a 1,3‐shift isomerization to give isothiocyanate intermediate D .…”

Highly Efficient and Practical Thiocyanation of Imidazopyridines Using an N‐Chlorosuccinimide/NaSCN Combination

“…2‐(3‐Bromophenyl)‐7‐methyl‐3‐thiocyanatoimidazo[1,2‐ a ]pyridine (4hd): Pale yellow solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 8.27 (d, J = 7.2 Hz, 1 H), 8.19 (s, 1 H), 7.98 (d, J = 7.6 Hz, 1 H), 7.55 (d, J = 8.0 Hz, 1 H), 7.47 (s, 1 H), 7.38–7.34 (m, 1 H), 6.94 (d, J = 6.8 Hz, 1 H), 2.47 (s, 3 H) ppm.…”

“…In 2015, Hajra et al developed the first example of a direct and environmentally benign system for the thiocyanation of imidazopyridines using eosin Y as a photoredox catalyst under ambient conditions . Subsequently, Wang's group independently disclosed a catalyst‐free highly regioselective C‐3 thiocyanation of imidazopyridines in the presence of K 2 S 2 O 8 , proceeding by a radical pathway …”

N‐Iodosuccinimide Catalyzed Oxidative Selenocyanation and Thiocyanation of Electron Rich Arenes

“…There are only a few methods available for selenocyanation of aromatic compounds using SeO 2 /malononitrile or CAN/KSeCN systems. Whereas, there are numerous methods available for thiocyanation of aromatic system which employ a variety of reagents such as oxone, aq HIO 5 , IBX,DDQ, I 2 photocatalysts and K 2 S 2 O 8 . However some of these methods suffer from disadvantages such as the need for stoichiometric or super stoichiometric amounts of catalysts or reagents, strong acidic or oxidizing conditions, limited substrate scope and toxicity of selenocyanating and thiocyanating sources.…”