Access to Amides and Lactams via Pyridotriazole as a Transformable Directing Group

Amide and lactam frameworks were synthesized via an efficient two-step strategy. In this protocol, pyridotriazoles were first treated with isocyanates to form the corresponding amides, which were found to be sufficiently reactive to undergo subsequent intramolecular N-H insertion in the absence of any additional reagents or catalysts.

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.

Transition Metal Catalyst-Free C-3 Sulfonylmethylation of Imidazo[1,2-a]pyridines with Glyoxylic Acid and Sodium Sulfinates in Water

Herein, we describe an efficient and benign protocol for direct C-3 sulfonylmethylation of imidazo[1,2-a]pyridines with glyoxylic acid and sodium sulfinates. Various sulfonylmethylated imidazo[1,2-a]pyridines were synthesized in water under transition metal catalyst-free conditions. This multicomponent reaction featured available substrates, good functional group tolerance, moderate to excellent yields, and mild reaction conditions.

Rhodium-catalyzed denitrogenative gem-difunctionalization of pyridotriazoles with thioesters: formal carbene insertion into C(O)-S bonds

A formal carbene insertion into C(O)-S bonds to access α-quaternary pyridines was achieved via a rhodium(II)-catalyzed in situ formation of sulfonium ylides from pyridotriazoles with thioesters followed by acyl group migration. This protocol has enabled an efficient denitrogenative gem-acylthiolation of pyridotriazoles to incorporate an acyl, pyridyl, and sulfur-substituted quaternary carbon center with high selectivity, broad substrate scope, and good functional group tolerance.

Copper-catalyzed three-component reaction to synthesize polysubstituted imidazo[1,2-a]pyridines

An efficient three-component one-pot and operationally simple cascade of 2-aminopyridines with sulfonyl azides and terminal ynones is reported, providing a variety of polysubstituted imidazo[1,2-a]pyridine derivatives in moderate to excellent yields. In particular, the reaction goes a through CuAAC/ring-cleavage process and forms a highly active intermediate α-acyl-N-sulfonyl ketenimine with base free.

Three-component one-pot synthesis of polysubstituted imidazo[1,2-a]pyridine derivatives through a base free CuAAC/ring-cleavage process.

Palladium-catalyzed oxidative C-H/C-H cross-coupling of pyrazolo[1,5-a]azines with five-membered heteroarenes

The use of Pd(OAc)₂ as the catalyst and AgOAc as the oxidant enabled the direct regioselective oxidative C-H/C-H cross-coupling of pyrazolo[1,5-a]pyrimidines or pyrazolo[1,5-a]pyridines with various five-membered heteroarenes without the need of pre-activation and/or directing groups. Successful coupling partners include thiophenes, benzothiophenes, thiazoles, furans, oxazoles, indoles and imidazo[1,2-a]pyridines.

Indium-mediated annulation of 2-azidoaryl aldehydes with propargyl bromides to [1,2,3]triazolo[1,5-a]quinolines

An efficient indium-mediated cascade annulation reaction of 2-azidoaryl aldehydes with propargyl bromides is reported. The aromatic 5/6/6-fused heterocycles, [1,2,3]triazolo[1,5-a]quinoline derivatives, could be constructed in one pot in moderate yields with a broad substrate scope. Mechanistic studies indicated that the reaction proceeded through allenol formation, azide-allene [3 + 2] cycloaddition, and dehydration. The synthetic potential of the products including the denitrogenative functionalization and the Pd-catalyzed coupling reactions has also been explored.

Co-Catalyzed Transannulation of Pyridotriazoles with Isothiocyanates and Xanthate Esters

An efficient radical transannulation reaction of pyridotriazoles with isothiocyanates and xanthate esters was developed. This method features conversion of pyridotriazoles into two N-fused heterocyclic aromatic systems-imino-thiazolopyridines and oxo-thiazolopyridine derivatives-via one-step Co(II)-catalyzed transannulation reaction proceeding via a radical mechanism. The synthetic usefulness of the developed method was illustrated in the synthesis of amino acid derivatives and further transformations of obtained reaction products.

Recent Advances in Denitrogenative Reactions of Pyridotriazoles

Diazo compounds display versatile reactivity and therefore are widely used in organic synthesis. Diazo compounds bearing a 2-pyridyl or a related azine moiety on the diazo carbon exist in the form of fused 1,2,3-triazoles. In this short review, we summarize the recent advances in denitrogenative reactions of [1,2,3]triazolo[1,5-a]pyridines (‘pyridotriazoles’) and related fused 1,2,3-triazoles. Over the past decade, there has been a surge of activity in this field, with novel denitrogenative reactions of pyridotriazoles induced by metal compounds, light, and Brønsted and Lewis acids having been devised. As a result, heterocyclic compounds and functionalized α-picolines as well as bio­active molecules have been synthesized. In the review, emphasis is also placed on the mechanisms of the new reactions.

1 Introduction

2 Ring-Chain Isomerization of Pyridotriazoles

3 Metal-Catalyzed Reactions

3.1 Rh(II) Catalysis

3.2 Rh(III) Catalysis

3.3 Cu Catalysis

3.4 Pd Catalysis

3.5 Catalysis by Other Metals

4 Metal-Free Reactions

5 Conclusion

Denitrogenative Transformations of Pyridotriazoles and Related Compounds: Synthesis of N-Containing Heterocyclic Compounds and Beyond

The high demand for new and efficient routes toward synthesis of nitrogen-containing heterocyclic scaffolds has inspired organic chemists to discover several methodologies over recent years. This Perspective highlights one standout approach, which involves the use of pyridotriazoles and related compounds in denitrogenative transformations. Readily available pyridotriazoles undergo ring-chain isomerization to produce uniquely reactive α-diazoimines. Such reactivity, enabled by metal catalysts, additives, or visible-light irradiation, can be applied in transannulation, insertion, cyclopropanation, and many other transformations.

Annulation of imidazo[1,2-a]pyridines under metal-free conditions

Synthesis of benzo[a]imidazo[5,1,2-cd]indolizines from 2-arylimidazo[1,2-a]pyridines and benzyne precursors under metal-free conditions has been described.