Domino Construction of Benzoxazole-Derived Sulfonamides via Metal-Free Denitrogenation of 5-Iodo-1,2,3-triazoles in the Presence of SO2 and Amines

Synthesis of Bench-stable Polycyclic Organophosphorus Heterocycles via Staudinger-type Annulations of ortho-Azidophenols

The formation of a five- or six-membered ring is known to stabilize unstable molecular structures such as hemiacetals. This idea can also be extended to stabilize other high-coordinated p-block element species. Herein, we synthesized two novel polycyclic organophosphorus heterocycles via Staudinger-type annulations. Reactions of either ortho-phosphinoarenesulfonyl fluorides 1 or ortho-phosphinobenzoic acid methyl esters 4 with ortho-azidophenols 2 gave rise to penta-coordinated P(V) heterocycles, benzo-benzo-1,2,3-thiazaphospholo-1,3,2-oxazaphosphole (B-B-TAP-OAP) 3 and benzo-benzo-1,2-azaphospholo-1,3,2-oxazaphosphol-12-one (B-B-AP-OAP) 5 in satisfactory yields. It is remarkable that heterocycles 3 and 5 are both bench-stable and exhibit considerable stability in a 10 % aqueous tetrahydrofuran solution. Preliminary computational studies disclosed that the formation of nitrogen gas is the key driving force for the annulations. In addition, the formation of a strong Si-F bond is another contributor to the annulation of 1 and 2.

Regioselective Synthesis of NO-Donor (4-Nitro-1,2,3-triazolyl)furoxans via Eliminative Azide-Olefin Cycloaddition

A facile and efficient method for the regioselective [3 + 2] cycloaddition of 4-azidofuroxans to 1-dimethylamino-2-nitroethylene under p-TSA catalysis affording (4-nitro-1,2,3-triazolyl)furoxans was developed. This transformation is believed to proceed via eliminative azide-olefin cycloaddition resulting in its complete regioselectivity. The developed protocol has a broad substrate scope and enables a straightforward assembly of the 4-nitro-1,2,3-triazole motif. Moreover, synthesized (4-nitro-1,2,3-triazolyl)furoxans were found to be capable of NO release in a broad range of concentrations, thus providing a novel platform for future drug design and related biomedical applications of heterocyclic NO donors.

Cascade Transformation of the Ansamycin Benzoquinone Core into Benzoxazole Influencing Anticancer Activity and Selectivity

The metal-free cascade transformation of geldanamycin benzoquinone core is proposed at relatively mild conditions. This approach yields new benzoxazole ansamycin antibiotics and enables their functionalization in an atom-economic manner, irrespective of the type of amine used. The analysis of the heterocyclization course reveals the dependence of its rate on the nature of the para-substituent within the benzylamine moiety (EDG/EWG) and the strength of the base. The reduction of the ansamycin core enables an increase in anticancer potency and selectivity.

Domino assembly of dithiocarbamates via Cu-catalyzed denitrogenative thiolation of iodotriazole-based diazo precursors

An efficient domino approach to assemble benzoxazoles and anthranilamides bearing dithiocarbamate moieties has been developed. The proposed route represents a Cu-catalyzed three-component reaction between readily available 5-iodo-1,2,3-triazoles, amines, and CS₂. The cascade transformation is based on a denitrogenative coupling of in situ formed dithiocarbamic acids with diazo intermediates, generated via annulation-triggered triazole ring-opening. This method is applicable to nucleophilic secondary amines and features good functional group compatibility.

Annulation-Triggered Denitrogenative Transformations of 2-(5-Iodo-1,2,3-triazolyl)benzoic Acids

The ability of [1,2,3]triazolobenzoxazinones to act as a source of "hidden" diazo group was discovered. These diazo precursors can be easily prepared by the intramolecular cyclization of 2-(5-iodo-1,2,3-triazolyl)benzoic acids. The Cu-catalyzed capture of the hidden diazo group allows for further functionalization through the denitrogenative pathway. The transformations proceed via the formation of either diazoimine or diazoamide intermediates. Novel routes to various anthranilamides as well as thiolated benzoxazinones were developed using the one-pot cyclization/diazo capture procedure.

Visible-Light-Catalyzed in Situ Denitrogenative Sulfonylation of Sulfonylhydrazones

A photocatalyzed in situ denitrogenative sulfonylation of N-arylsulfonyl hydrazones has been developed. This transformation provides a low-carbon strategy to assemble arylalkyl sulfones in a stepwise denitrogenation/sulfonylation manner.