Catalytic Thiourea Promoted Electrophilic Thiocyanation of Indoles and Aromatic Amines with NCS/NH₄SCN

Abstract

A simple and efficient protocol for the electrophilic thiocyanation of indoles and aromatic amines with thiourea/NCS/NH 4 SCN system has been developed. The major features of the present procedure are the mild conditions, good yields, short reaction times, and the use of inexpensive and readily available organocatalyst. Moreover, N-chlorosuccinimide (NCS) was found to be indispensable, and thiourea could greatly promote the reaction.

Sustainable Synthetic Approaches Involving Thiocyanation and Sulfur- Cyanation: An Update

“…Among the various modifications of these structures, the introduction of a thiocyanate function has been studied. The direct C-H thiocyanation was achieved by using a combination of sodium thiocyanate as the SCN source and N-chlorosuccinimide (NCS) as the oxidant, affording 3-thiocyanatoimidazo[1,2-a]pyridines (8) in good to excellent yields (Scheme 5) [5]. Ethanol was used as a green and efficient reaction solvent.…”

“…As mentioned previously ( §2.1.1), anilines can be thiocyanated through direct functionalization of the aromatic ring using the thiocyanate anion [7][8][9]. Usually, the cyanation takes place at the para position, however, when this position is substituted, the second favored position becomes the ortho one and in that case, a subsequent cyclization via the nucleophilic attack of the nitrogen of the aniline on the cyano group of the SCN can occur to form the corresponding aminobenzothiazole (78) (Scheme 33).…”

“…Thiourea has also been used in a catalytic amount to accelerate the formation of N-thiocyanatosuccinimide from NCS and NH 4 SCN (Scheme 8) [8]. By using this system, the thiocyanation of indoles and aromatic amines led to the corresponding thiocyanates in good yields.…”

Selectfluor-initiated cyanation of disulfides to thiocyanates

“…Much effort has been made toward the synthesis of thiocyanates so far. Generally, thiocyanates can be synthesized via the following two major routes (Scheme 1(a)): (1) thiocyanation of organic partners (arenes, organic halides, diazonium salts, and arylboronic acids) in the presence of inorganic thiocyanates 10–15 and (2) cyanation of organosulfur compounds including thiols, disulfides, and sulfinates with electrophilic and nucleophilic cyanation reagents. 16–20 Thiocyanates can also be prepared via CuCN-mediated direct aerobic oxidative cyanation of thiophenols and diaryl disulfides.…”

An Efficient Selectfluor-Mediated Oxidative Thio- and Selenocyanation of Diversely Substituted Indoles and Carbazoles

“…Aryl thio-and selenocyanates are versatile intermediates for various sulfur-and selenium-containing compounds that are of synthetic and biological interest [14][15][16][17][18][19][20][21][22][23][24][25][26]. Aryl thiocyanates are widely employed as building blocks in the synthesis of diverse sulfides [27,28], thiocarbamates [29], thionitriles [30], sulfonic acids [31], sulfonyl chlorides [32], thioesters [33], and sulfonyl cyanides [31] and mainly in the synthesis and functionalization of heterocyclic compounds [25,26,[34][35][36][37][38][39][40]. Particularly, selenium-containing organic compounds have recently attracted the interest of the scientific community due to their promising chemopreventive properties in connection with cancer therapy [32,[41][42][43][44], and also as antioxidant agents [45,46].…”