Metal-free oxidative cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen

Abstract

Aerobic cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen under metal-free conditions.

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

“…First, Deng et al disclosed in the same time their study focused on the use of 2-aminobenzothiazoles 326 as 1,3-bis-nucleophile in place of 2-aminopyridines under aerobic conditions in DMSO at temperature up to 130°C (Scheme 117). [144] The reaction involved in only one equivalent of sulfur, suggesting that bot oxygen and DMSO could act as complementary oxidants. The reaction was found to be less efficient when performed under argon.…”

Tri‐Functional Elemental Sulfur Enabling Bis‐Heteroannulation of Methyl Ketoximes with Methyl N‐Heteroarenes

“…[6] Consequently, the development of synthetic methods for sulfur-heterocycles has attracted considerable interests in molecular synthesis. [7] In the past decade, cheap, nontoxic and bench-stable elemental sulfur has found versatile functionalities to be an effective moderator to facilitate the formation of nitro-containing heterocycles [8] as well as one of the viable sulfur sources to construct sulfur-heterocycles [9] ( Figure 1a). For example, Nguyen and co-workers have developed a highly atom-economical approach for benzimidazole formation with S 8 as a redox moderator from 2-amino nitrobenzenes and methyl aza-arenes.…”

“…An inorganic base and dimethyl sulfoxide (DMSO) as reaction media were both found to be essential. Among those bases tested, cesium carbonate featured the best efficiency, and the desired product 3 a was formed in 70% yield (entries [5][6][7][8][9]. Other organic solvents screened including dimethylformamide (DMF), N-methylpyrrolidone (NMP), 1,4dioxane, toluene, and dichloroethane (DCE) all completely prohibited the reaction (entries [10][11][12][13][14].…”

Metal‐Free Synthesis of Imidazo[2,1‐b]thiazoles from Thioimidazoles and Ketones Mediated by Selectfluor

“…[4] In view of the importance of imidazo[2,1-b]thiazole derivatives, a number of procedures have been developed to prepare them. [5] According to literature reports, 2-aminobenzothiazoles could yield imidazo [2,1-b]thiazole molecules via the heterocyclization reaction with traditional α-bromoketone, [6] aryl methyl ketones, chalcones, [7] cyclic ketones, [8] 2-phenoxyacetophenones, [9] aryl aldehydes coupled with alkynes, [10] aryl aldehydes coupled with isocyanides, [11] and so on. [12] On the other hand, 2-mercaptobenzoimidazoles were also able to afford this class of heterocyclic compounds through the annulation reactions with terminal alkynes, [13] Nitroalkenes, [14] dihaloalkenes.…”