Umpolung Strategy with 2‐Aminothiophenols: Access to 2‐Arylbenzothiazine Derivatives from Alkyl Aryl Ketones

Abstract

Strong Brønsted acids were found to catalyze the oxidative condensation of 2-aminothiophenols with aryl alkyl ketones in DMSO to provide a wide range of complex 2-arylbenzothiazines. With acetophenones, dimeric 2-arylbenzothiazines were formed. On the other hand, the reaction with propiophenones resulted in 2:1 adducts whereas 1:1 adducts were produced with isobutyrophenones, benzoylacetonitrile and ethyl benzoylacetate.

Nucleophile-induced ring contraction in pyrrolo[2,1-c][1,4]benzothiazines: access to pyrrolo[2,1-b][1,3]benzothiazoles

“…However, recently, we have reported a new class of FPDs, aroylpyrrolobenzothiazinetriones (APBTTs) 1 ( Figure 2 ) [ 37 – 38 ], whose structural features allowed us to assume a possibility of the development of a new approach to PBTAs via a nucleophile-induced ring contraction in the 1,4-benzothiazine moiety of compounds 1 ( Scheme 5 ). Firstly, FPDs 1 bear a 1,4-benzothiazine moiety that is known to be prone to undergo a ring contraction reaction to afford the corresponding 1,3-benzothiazole derivatives under the action of nucleophiles [ 39 – 42 ], oxidizing agents [ 43 – 48 ] or ultraviolet irradiation [ 49 ]. Secondly, the presence of a highly reactive thioester group C 4 =O [ 50 ] in FPDs 1 made us to expect the position C 4 ( Figure 2 ) to be the most reactive electrophilic center in these molecules, which would also contribute to the development of a new synthetic approach to PBTAs.…”

Silver-Catalyzed Skeletal Editing of Benzothiazol-2(3H)-ones and 2-Halogen-Substituted Benzothiazoles as a Rapid Single-Step Approach to Benzo[1,2,3]thiadiazoles

“…During our research on the preparation of novel two-photon absorbing materials, we serendipitously found that 2-chlorobenzothiazoles ( 2 ), upon treatment with excess of AgNO 2 in aprotic polar organic solvents such as DMSO, DMF, or MeCN, undergo direct conversion to benzo­[1,2,3]­thiadiazoles ( 1 ) instead of forming 2-nitrobenzothiazoles (Scheme b). This unexpected but valuable ring transformation enabling the preparation of iBTD without the need for using 2-aminobenzenethiols (which are difficult to work with due to their pungent smell, toxicity, and sensitivity toward oxidation) led us to investigate this skeletal editing reaction further and find optimal reaction conditions and expedient reagents to be applied in the efficient/larger scale synthesis. In this regard, we report herein a silver­(I)-promoted transformation of 2-chlorobenzothiazoles and benzothiazol-2­(3 H )-ones using NaNO 2 as a cheap reagent for the facile synthesis of benzo­[1,2,3]­thiadiazoles ( iBTD ).…”

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

“…Recently, Nguyen and Retailleau introduced a TFA-catalyzed umpolung strategy with 2-aminothiophenols, preparing several 2H-benzo-1,4-thiazine derivatives 5 in high yield [28]. 3-Phenyl-2H-benzo-1,4-thiazine, an earlier representative of this family, was found to transform into a green-blue chromophore in the presence of peroxides or redox-active metal ions under acidic conditions, creating a potential detection method for such entities [29].…”