Synthesis of 4‐Aryl‐1,2,3‐Thiadiazoles via NH₄I‐Catalyzed Cyclization of N‐Tosylhydrazones with Sulfur

Abstract

A simple and practical NH 4 I-catalyzed cyclization of N-tosylhydrazones with sulfur in the presence of TBHP as organic oxidant was developed. 4-aryl-1,2,3-thiadiazole were obtained in moderate to excellent yields, even on gram scale. This methodology has great advantages including cheap iodine source, avoiding the use of inorganic oxidant, short reaction time, wide substrate scope, and high functional groups tolerance.

Recent Advances in the Synthesis of Heterocycles via Reactions Involving Elemental Sulfur

“…1,2,3 All four reported methods were based on redox catalysis of I 2 /I À couple. Suitable oxidant or oxidation conditions could be applied for recycling of I 2 from I À , including K 2 S 2 O 8 , [112] TBHP [115] as well as more sophisticated electrolytic [113] or flavin-catalyzed aerobic [114] conditions. Mechanistically, the first step was an iodination of the methyl group of 253 into 255 to facilitate the introduction of sulfur chain to the carbon skeleton.…”

Recent Advances in Sulfur-Containing Heterocycle Formation via Direct C–H Sulfuration with Elemental Sulfur

“…4-Aryl-1,2,3-thiadiazoles could be obtained by iodidecatalyzed oxidative cyclization of N-tosylhydrazones with element sulfur in the presence of different oxidants (Scheme 50). K 2 S 2 O 8 , 80a oxygen 83 or TBHP 84 displayed the capacity to re-oxidize Ito catalytically active I 2 , which enabled this transformation. Additionally, an electrochemical protocol employed mass free electrons as reagents to oxidize iodine anion to I 2 without using excess amounts of external oxidant.…”

I2/DMSO-Catalyzed Transformation of N-tosylhydrazones to 1,2,3-thiadiazoles

“…Recently, N-tosylhydrazones, which are readily accessible and inexpensive chemicals, have attracted much attention in the construction of heterocyclic compounds (Xia and Wang, 2017). In particular, iodine-catalyzed cyclization of N-tosylhydrazone with elemental sulfur has become one of the most efficient methods to synthesize 4-aryl-1,2,3-thiadiazoles (Chen et al, 2015;Ishikawa et al, 2017;Liu et al, 2018;Li et al, 2019). This transformation was triggered by α-iodation of acetophenone tosylhydrazone, which was generated in situ from the corresponding precursors (Scheme 1).…”

“…To avoid the detrimental effect of acidic HI, and also to facilitate progress of a catalytic reaction, in the previous reports, an oxidizing reagent was adopted to convert HI to I 2 . With this strategy, some effective systems, such as K 2 S 2 O 8 /TBAI (Scheme 1, method a; Chen et al, 2015), TBHP/NH 4 I (method b; Li et al, 2019), and flavin-catalyzed O 2 oxidation/NH 4 I (method c; Liu et al, 2018), have been developed successfully. Electrochemical oxidation in the combination of using NH 4 I as additive was also proved to be effective (method d; Ishikawa et al, 2017).…”