A catalyst-free method for the synthesis of 1,4,2-dithiazoles from isothiocyanates and hydroxylamine triflic acid salts

Isothiocyanates: happy-go-lucky reagents in organic synthesis

Owing to their unique structural features, isothiocyanates (ITCs) are a class of highly useful and inimitable reagents as the -NCS group serves both as electrophile and nucleophile in organic synthesis. ITCs share a rich legacy in organic, medicinal, and combinatorial chemistry. Compared to their oxygen equivalents, isocyanates, ITCs are easily available, less unpleasant, and somewhat less harmful to work with (mild conditions) which makes them happy-go-lucky reagents. Functionalized ITCs can finely tune the reactivity of the -NCS group and thus can be exploited in the late-stage functionalization processes. This review's primary aim is to outline ITC chemistry in the construction and derivatization of heterocycles through the lens of sustainability. For ease and brevity, the sections are divided based on reactive centers present in functionalized ITCs and modes of cyclisation. Scrutinizing their probable unexplored directions for future research studies is also addressed.

Iron(III)-Catalyzed Regioselective Synthesis of Electron-Rich Benzothiazoles from Aryl Isothiocyanates via C-H Functionalization

We report herein a direct synthetic route for the preparation of 2-arylbenzothiazoles using aryl isothiocyanates and electron-rich arenes. The synthetic route involves triflic acid promoted addition of the arenes to aryl isothiocyanates followed by FeCl₃-catalyzed C-S bond formation via C-H functionalization. The approach provides the advantage of synthesis of benzothiazoles without the conventional use of aryl aldehyde/carboxylic acid precursors employing the less expensive iron(III) catalyst.

An Aminative Rearrangement of O-(Arenesulfonyl)hydroxylamines: Facile Access to ortho-Sulfonyl Anilines

Ortho-sulfonyl anilines are important building blocks for a range of applications. We report the discovery of an aromatic rearrangement reaction of O-(arenesulfonyl)hydroxylamines which leads directly to ortho-sulfonyl anilines through formation of a new C-N bond with excellent levels of regiocontrol for the ortho position(s) over all others. We establish that the rearrangement is proceeding through an intermolecular mechanism and propose that the regiocontrol observed is the result of attractive non-covalent interactions occurring during the C-N bond-forming step. Importantly, this method is complementary to classical aniline sulfonation in terms of the variously substituted regioisomers that can be obtained and it is also applicable to O-(benzylsulfonyl) hydroxylamines.

O-Protected NH-free hydroxylamines: emerging electrophilic aminating reagents for organic synthesis

In this highlight, O-protected NH-free hydroxylamine derivatives have been evaluated in the construction of nitrogen-enriched compounds, such as primary amines, amides, and N-heterocycles, with high regio-, chemo- and stereoselectivity in the unprotected form, showcasing the late-stage functionalization of natural products, drugs and functional molecules by biocatalysis, organocatalysis, and transition metal catalysis. The reactivity dichotomy among these N-O reagents has been explored based on SET and metal-nitrenoids.