Radical Route to 1,4-Benzothiazine Derivatives from 2-Aminobenzenethiols and Ketones under Transition-Metal-Free Conditions

Abstract

Transition-metal-free radical access to 1,4-benzothiazine derivatives from o-aminobenzenethiols is disclosed. This procedure is available for various ketones including α,β-unsaturated, cyclic, linear, and fluoroalkyl ketones to generate a number of 1,4-benzothiazines, which exist in numerous bioactive and natural molecules, rendering this protocol attractive to both synthetic and medicinal chemistry.

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

“…In this context, the development of new conditions allowing direct access to original 2‐aryl‐1,4‐benzothiazine motif from 2‐aminothiophenols and aryl alkyl ketones would be highly desirable [5] . Taking advantage of the facile oxidation of the thiols into the corresponding disulfide and the acid‐catalyzed condensation of an amino group with a ketone group, we suggest here the use of 2‐aminothiophenols 1 for direct oxidative functionalization of readily available enolizable ketones via an in‐situ and easily reversal of polarity of 1 from a 1,2‐bis‐nucleophile to 1,2‐nucleophile/electrophile.…”

“…On the other hand, the background reaction conditions could result in higher yield (21%) of 3 aa at a higher temperature (100°C) (entry 3). When a base such as DBU [5] or cyclohexylamine was used as a catalyst (entry 4) or additive (entry 5), the reactions in both cases stopped at the formation of monomer 3-phenyl-2H-benzo[b] [1,4]…”

Bioinspired Heterocyclic Partnership in a Cyanine-Type Acidichromic Chromophore

“…Starting from this background it was argued that novel functional chromophores could be obtained by reaction of the nucleophilic enamine-type C2 position of the 2 H -1,4-benzothiazine moiety [ 35 , 36 , 37 ] with carboxaldehydes of nitrogenous heterocyclic aromatic systems. This would allow the build-up of a variant of the benzothiazine-based cyanine chromophore, with the benzothiazine nitrogen acting as acceptor and the nitrogen of the heterocyclic aromatic system as donor component.…”

Facile preparation of dihydro-1,4-benzothiazine derivatives via oxidative ring-expansion of 2-aminobenzothiazoles with olefins

“…Cossy et al 5 described a FeCl 3 -catalyzed intramolecular nucleophilic cyclization to construct the 1,4-benzothiazine skeleton via a carbocation intermediate (Scheme 1b). Yi and co-workers 6 reported a radical involving annulation strategy to access 1,4-benzothiazine derivatives from feedstock of 2-aminobenzenethiols and ketones (Scheme 1c).…”