Synthesis of 1,4-benzothiazinones from acylpyruvic acids or furan-2,3-diones and o-aminothiophenol

The Multifaceted Opportunities Provided by the Pheomelanin-Inspired 1,4-Benzothiazine Chromophore: A Still-Undervalued Issue

1,4-Benzothiazines are the main building blocks of the naturally occurring pheomelanin pigments, and their chromophoric properties have been strongly related to the well-known phototoxicity of these pigments, partly responsible for the high incidence of melanoma and other skin cancers in red-haired people. However, some peculiar features of the 1,4-benzothiazine chromophore could be functionally exploited in several sectors. Within this context, in this perspective, an overview of the very recently reported applications of the 1,4-benzothiazine chromophore in pH sensing, filter permeability control, smart packaging, electrochromic device fabrication, bioimaging, photocatalysis, and HPLC detection systems is provided, together with a brief presentation of recently developed synthetic approaches to the 1,4-benzothiazine scaffold, with the aim of emphasizing the still-undervalued multifunctional opportunities offered by this class of compounds.

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

Pyrrolo[2,1-b][1,3]benzothiazoles are an important class of fused sulfur and nitrogen-containing heterocycles intensively studied in medicinal chemistry and pharmacology. In the present paper, a new synthetic approach to pyrrolobenzothiazoles is developed based on 1,4-thiazine ring contraction in 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones under the action of nucleophiles. The proposed approach works well with alkanols, benzylamine, and arylamines. The scope and limitations of the developed approach are studied. The synthesized pyrrolobenzothiazole derivatives represent an interest to pharmaceutics, since their close analogs show CENP-E inhibitory activity, interesting for the targeted cancer therapy development.

Continuous Flow Synthesis of 1,4-Benzothiazines Using Ambivalent Reactivity of (E)-β-Chlorovinyl Ketones: A Point of Reaction Control Enabled by Flow Chemistry

A continuous flow system to 1,4-benzothiazines was developed using the point of reaction control, where the ambivalent (E)-β-chlorovinyl ketones and 2,2'-dithiodianilines were confined in a diffusion controlled flow setting. The successful segregation of reactive chemical species in a flow setting allowed more defined reaction pathways that are not feasible in traditional batch reaction conditions. The point of reaction control in flow systems helps to execute the reactions often plagued with the concurrent generation of multiple chemical species.

On the Question of Stepwise [4+2] Cycloaddition Reactions and Their Stereochemical Aspects

Even at the end of the twentieth century, the view of the one-step [4+2] cycloaddition (Diels-Alder) reaction mechanism was widely accepted as the only possible one, regardless of the nature of the reaction components. Much has changed in the way these reactions are perceived since then. In particular, multi-step mechanisms with zwitterionic or diradical intermediates have been proposed for a number of processes. This review provided a critical analysis of such cases.