Conversion of thiobenzamides to benzothiazoles via intramolecular cyclization of the aryl radical cation

Recent advances in sulfur- and phosphorous-centered radical reactions for the formation of S–C and P–C bonds

“…The Bose group introduced a series reagents such as Dess-Martin periodinane (DMP), 72 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) 73 to promote the cyclization of thioformanilides. Downer-Riley and Jackson employed phenyliodine(III) bis(trifluoroacetate)(PIFA) and CAN to generate aryl radical cation intermediates from thioformanilides for the synthesis of benzothiazoles 74. The Penenory group reported chloranil-induced olefin-co-oxygenation (TOCO) reactions.78 The Posner and Bachi groups employed this kind of reactions for the synthesis of sulfonated 2,3-dioxabicyclo[3.3.1]nonanes (Scheme 33).…”

Untitled

“…Downer et al, have introduced a new and applicable protocol for the intramolecular cyclization of thiobenzamides to benzothiazoles through the aryl radical cations as reactive intermediates (Scheme 25, Method 3) 54 . The protocol uses phenyliodine (III)bis(trifluoroacetate) (PIFA) in trifluoroethanol or cerium ammonium nitrate (CAN) in aqueous acetonitrile to enhance the cyclization within 30 min at room temperature, which afforded moderate yield of the products.…”

Switching reaction pathways of trifluoromethylated thiobenzanilides by choice of different oxidative systems

“…Traditional methods for their syntheses involve the condensation of o-aminothiophenols with substituted carboxylic acids, aldehydes, nitriles, or esters, but such methods suffer from difficulties in the preparation of readily oxidizable o-aminothiophenol precursors [2]. Alternatively, oxidative cyclization of thiobenzanilides has been the most frequently used route to synthesize benzothiazoles with various oxidants such as potassium ferricyanide(III) [3], cerium(IV) ammonium nitrate (CAN) [4], hypervalent iodine reagents (DMP, PIFA) [5], 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) [6], and manganese(III) triacetate [7]. Recently, palladium or copper catalyzed coupling reactions to construct benzothiazoles via C-S bond formation from ortho-haloanilides have been developed [8].…”