Synthesis of Polysubstituted Furans via Rh(II)-Catalyzed [2 + 3] Annulation of N-Sulfonyl-1,2,3-triazoles with Enaminones

An unprecedented [2 + 3] annulation of N-sulfonyl-1,2,3-triazoles with enaminones is reported for the access of polysubstituted furans. The key to the success of the transformations lies in the use of Rh(II)-Brønsted acid as cooperative catalysts. Unlike the conventional annulations of N-sulfony-l-1,2,3-triazoles, the Rh(II)-azavinyl carbenes species play dual functions in this work, enabled by the cleavage of the C(sp2)-N bond. The mechanism studies suggested that an intermolecular rearrangement of the TsNH- group is crucial to the annulation process.

Substituent-Controllable Cascade Regioselective Annulation of β-Enaminones with N-Sulfonyl Triazoles for Modular Access to Imidazoles and Pyrroles

A controllable synthesis of trisubstituted imidazoles and pyrroles has been developed through rhodium(II)-catalyzed regioselective annulation of N-sulfonyl-1,2,3-trizaoles with β-enaminones. The imidazole ring was formed through a 1,1-insertion of the N-H bond to α-imino rhodium carbene, followed by a subsequent intramolecular 1,4-conjugate addition. This occurred when the α-carbon atom of the amino group was bearing a methyl group. Additionally, the pyrrole ring was constructed by utilizing a phenyl substituent and undergoing intramolecular nucleophilic addition. The mild conditions, good tolerance towards functional groups, gram-scale synthesis capability, and ability to undergo valuable transformations of the products qualify this unique protocol as an efficient tool for the synthesis of N-heterocycles.

Access to (Z)-β-Substituted Enamides from N1-H-1,2,3-Triazoles

A direct ring-opening/nucleophilic substitution reaction of N1-H-1,2,3-triazoles has been described. Divergent (Z)-β-halogen- or sulfonyl-substituted enamides could be stereospecifically synthesized in a tunable manner. This strategy might not only enable a new ring-opening method of N1-H-1,2,3-triazoles under nonmetal catalysis and mild reaction conditions but also offer a good opportunity to reliably access versatile (Z)-β-substituted enamides that could be used as synthetic precursors for further synthetic transformations.

Synthesis of α-cyano sulfone via thermal rearrangement of 1,4-disubstituted triazole mediated by carbene and radical species

α-Cyano sulfone is produced conveniently from 1,4-disubstituted triazole, which involves carbene, ketenimine and radical species as the key intermediates.

Cascade Rh(ii) and Yb(iii) catalyzed synthesis of substituted naphthofurans via transannulation of N-sulfonyl-1,2,3-triazoles with β-naphthols

Synthesis of substituted naphthofurans has been achieved via an efficient cascade Rh(ii)/Yb(iii) catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with β-naphthols.

Synthesis of α-aminoketones from N-sulfonyl-1,2,3-triazoles via N-sulfinyl imines generated by intramolecular oxygen transfer

A sulfinyl imine was generated by intramolecular oxygen transfer of an α-iminocarbene, which led to an α-aminoketone via nucleophilic addition and oxidation.

Metal-Free Synthesis of (E)-Monofluoroenamine from 1-Sulfonyl-1,2,3-triazole and Et2O·BF3 via Stereospecific Fluorination of α-Diazoimine

A general, stereospecific, and straightforward method for the rapid preparation of functionalized (E)-monofluoroenamines is reported. Rather than transition metals (Rh, Ni, Pd, Cu, Ag, etc.), Et₂O·BF₃ was employed to promote the formation of α-diazoimine through the Dimroth equilibrium of common 1-sulfonyl-1,2,3-triazole for the first time. An overall migration of fluoride from boron to the diazo-linked carbon of α-diazoimine was achieved. Derivations and late-stage modification of bioactive molecule were conducted. A plausible mechanism was also proposed.

Metal-free synthesis of 2-aminonaphthalenes by intramolecular transannulation of 1-sulfonyl-4-(2-alkenylphenyl)-1,2,3-triazoles

A facile metal-free synthesis of naphthalenes by intramolecular transannulation of 1-sulfonyl-4-(2-alkenylphenyl)-1,2,3-triazoles was realized. The in situ formed ketenimine was proposed as the key intermediate, and the desired 2-aminonaphthalenes were generated in up to 87% yield in refluxing 1,2-dichloroethane without any catalyst or additive.

Diversity-oriented synthesis of heterocycles and macrocycles by controlled reactions of oxetanes with α-iminocarbenes

Using N-sulfonyl triazoles as substrates, compounds as diverse as 2-imino tetrahydrofurans, 13- and 15-membered ring aza-macrocycles can be prepared selectively via formal [1 + 4], [5 + 4 + 4] and [3 + 4 + 4 + 4] condensations of α-imino carbenes and oxetanes under Rh(ii)-catalysis or thermal activation. Spirocyclic N-heterocycles are also accessible by means of Buchwald-Hartwig and Pictet-Spengler cyclizations. By reaction control, substrate selection or further derivatization, a large variety of chemical structures is thus achievable. Finally, using triazoles reacting under thermal activation, interesting mechanistic insight was obtained.

Rhodium-catalyzed synthesis of 1,2-dihydropyridine by a tandem reaction of 4-(1-acetoxyallyl)-1-sulfonyl-1,2,3-triazole

A tandem reaction of 4-(1-acetoxyallyl)-1-sulfonyl-1,2,3-triazole involving α-imino rhodium carbene was reported and 1,6-dihydropyridin-3-yl acetate was obtained.

Synthesis of Multifunctionalized 2-Carbonylpyrrole by Rhodium-Catalyzed Transannulation of 1-Sulfonyl-1,2,3-triazole with β-Diketone

A facile rhodium-catalyzed transannulation of 1-sulfonyl-1,2,3-triazoles with β-diketones was realized, and a series of multisubstituted 2-carbonylpyrroles were synthesized efficiently (up to 94% yield). The protocol features several advantages, such as readily available materials, mild reaction conditions, a concise operating procedure, a broad reaction scope, and excellent regioselectivity when benzoylacetone derivatives were used.

Synthesis of 5-Iodo-1,2,3,4-tetrahydropyridines by Rhodium-Catalyzed Tandem Nucleophilic Attacks Involving 1-Sulfonyl-1,2,3-triazoles and Iodides

Sodium iodide is used for the first time as a nucleophile to trap an α-imino rhodium carbene, which triggers a tandem process involving intermolecular nucleophilic attack and intramolecular S_N2 reaction. A series of 5-iodo-1,2,3,4-tetrahydropyridines are obtained in high yield, and the synthetic utility of the products is demonstrated in cross-coupling reactions and the construction of biorelated polycyclic compounds.

Lewis Acid-Catalyzed Denitrogenative Transannulation of Pyridotriazoles with Nitriles: Synthesis of Imidazopyridines

The synthesis of imidazo[1,5-a]pyridines through denitrogenative transannulation of pyridotriazoles with nitriles using BF₃·Et₂O as catalyst has been described. The combination of solvents (dichlorobenzene-dichloroethane) plays a crucial role in achieving quantitative yields of desired products under metal-free conditions.

Copper-Catalyzed Denitrogenative Transannulation Reaction of Pyridotriazoles: Synthesis of Imidazo[1,5-a]pyridines with Amines and Amino Acids

The copper-catalyzed aerobic oxidative synthesis of imidazo[1,5-a]pyridines via cascade denitrogenative transannulation reaction of pyridotriazoles with benzylamines with good functional group tolerance is developed. The present methodology is also applicable to amino acids to obtain imidazo[1,5-a]pyridines via decarboxylative oxidative cyclization.

Rhodium(II) Azavinyl Carbenes and their Recent Application to Organic Synthesis

This highlight solely focusses on the synthetic applications of azavinyl rhodium(II) carbenes derived from N-sulfonyl triazoles. An overview of their use in intermolecular reactions to form a variety of heterocycles is examined, in addition to intramolecular annulations and rearrangements.

Chiral dirhodium catalysts derived from l-serine, l-threonine and l-cysteine: design, synthesis and application

A series of dirhodium complexes were synthesized and found to be effective chiral catalysts for nitrene and carbene transfer reactions.