Complex Annulations through Silver Carbenoid Intermediate: An Alternative Entry to Transformations of 1,2,3-Triazoles

Cu(II)-Catalyzed Annulative Sulfonylimination of α-Carbonyl-γ-alkynyl Sulfoxonium Ylides through Sulfoxonium Ylide Elimination for Access to (Z)-1H-Isochromenes

1H-Isochromene scaffolds are ubiquitous in natural products and significant bioactive molecules. Although several methods for these molecular syntheses have been developed, reports on the efficient construction of iminated isochromenes are still rather limited. Herein, we report a new Cu(II)-catalyzed annulation and sulfonylimination cascade of α-carbonyl-γ-alkynyl sulfoxonium ylides with sulfamides, enabling direct C-C σ-bond elimination to furnish iminated (Z)-1H-isochromenes in 51-97% yields. During the reaction process, the sulfoxonium ylide unit as a traceless eliminative group is the key to successful sulfonylimination, which enables Cu(II)-catalyzed N-H insertion and subsequent acetic acid-mediated C-C σ-bond elimination.

Copper-Catalyzed Nitrogen Atom Transfer to Isoquinolines via C-N Triple Bond Cleavage and Three-Component Cyclization

A copper(I)-catalyzed tandem reaction of 2-bromoaryl ketones, terminal alkynes, and CH₃CN is developed, which combines N atom transfer and three-component [3 + 2 + 1] cyclization, and efficiently produces densely functionalized isoquinolines in a facile, highly selective, and general manner. In the reaction, the formation of aromatic C-N bonds along with the complete C-N triple bond cleavage is first realized; Cu(III)-acetylide species might serve as the intermediates, which allow highly selective 6-endo-dig cyclization.

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.

Acid-catalyzed ring-expansion of 4-(1-hydroxycyclobutyl)-1,2,3-triazoles

A direct ring-opening/semipinacol rearrangement reaction catalyzed by the Brønsted acid of 4-(1-hydroxycyclobutyl)-1,2,3-triazole is reported, in which the usage of metal catalysts and the reservation of sulfonyl groups are avoided.

Reaction Outcome Critically Dependent on the Method of Workup: An Example from the Synthesis of 1-Isoquinolones

A striking dependence on the method of workup has been found for annulation of benzonitriles ArC≡N to N-methyl 2-toluamide (1), facilitated by n-BuLi (2 equiv): quenching the reaction by a slow addition of water produced the expected 1-isoquinolones 2; by contrast, slow pouring of the reaction mixture into water afforded the cyclic aminals 5 (retaining the NMe group of the original toluamide). The mechanism of the two processes is discussed in terms of the actual H⁺ concentration in the workup. Both 2 and 5 were then converted into the corresponding 1-chloroisoquinolines 3, coupling of which, mediated by (Ph₃P)₂NiCl₂/Zn, afforded bis-isoquinolines 4.

Asymmetric Intramolecular Dearomatization of Nonactivated Arenes with Ynamides for Rapid Assembly of Fused Ring System under Silver Catalysis

Arene dearomatization is a straightforward method for converting an aromatic feedstock into functionalized carbocycles. Enantioselective dearomatizations of chemically inert arenes, however, are quite limited and underexplored relative to those of phenols and indoles. We developed a method for diazo-free generation of silver-carbene species from an ynamide and applied it to the dearomatization of nonactivated arenes. Transiently generated norcaradiene could be trapped by intermolecular [4 + 2] cycloaddition, synthesizing polycycles with five consecutive stereogenic centers. This protocol constitutes the first highly enantioselective reaction based on the diazo-free generation of silver-carbene species. Mechanistic investigations revealed a dearomatization followed by two different classes of pericyclic reactions, as well as the origin of the chemo- and enantioselectivity.

Synthesis of ortho-arylated and alkenylated benzamides by palladium-catalyzed denitrogenative cross-coupling reactions of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids

An efficient palladium-catalyzed denitrogenative cross-coupling reaction of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids is described. The reaction affords various ortho-aryl and alkenylated benzamides in good to high yields.

BF3·Et2O catalyzed transannulation of pyridotriazoles with isothiocyanates: synthesis of thiazolo[3,4-a]pyridin-3-imines

The synthesis of thiazolo[3,4-a]pyridin-3-imines, through denitrogenative transannulation of pyridotriazoles, under transition metal-free conditions is described.

Construction of fluorescence active MOFs with symmetrical and conformationally rigid N-2-aryl-triazole ligands

1,4-Bis-triazole-substituted arene (NAT) was designed and synthesized for the construction of metal organic frameworks. Unlike the tri-phenyl analogs, which give a twisted conformation between three benzene rings due to the A-1,3 repulsion, the NAT-ligand gave the energetically favored co-planar conformation with the strong fluorescence emission. With this ligand, two new MOFs, NAT-MOF-Cd (2,3,4-c) and NAT-MOF-Cu (4-c), were successfully obtained with the structure confirmed by X-ray. With the six-coordinated Cd(ii) cluster, an interesting metal–ligand coordination and H-bonding hybridized porous polymeric structures were observed. In contrast, a typical Cu(ii) paddle wheel coordination was obtained with NAT and Cu, giving a new MOF structure with moderate stability in aqueous solution from pH 1–11 for 24 hours, which suggests a promising future for applications in fluorescence sensing and photocatalysis.

1,4-Bis-triazole-substituted arene (NAT) was designed and synthesized for the construction of fluorescent metal organic frameworks.

Regioselective N1- and N2-heterocycloalkylation of N1-sulfonyl-1,2,3-triazoles

A tuneable and visible-light-driven three-component reaction between N¹-sulfonyl-1,2,3-triazoles, saturated heterocycles, and N-bromosuccinimide for regioselective synthesis of N¹- or N²-heterocycloalkylated 1,2,3-triazoles.

Pd-Catalyzed regioselective synthesis of 2,6-disubstituted pyridines through denitrogenation of pyridotriazoles and 3,8-diarylation of imidazo[1,2-a]pyridines

Synthesis of 2,6-disubstituted pyridines from pyridotriazoles through palladium-catalyzed aerobic oxidative denitrogenative reactions has been described.

Diastereoselective access to 2-aminoindanonesviathe rhodium(ii)-catalyzed tandem reaction involving O–H insertion and Michael addition

A rhodium(ii)-catalyzed tandem reaction involving O–H insertion ofN-sulfonyl 1,2,3-triazoles and Michael addition has been described. A series of 2-amino-1-indanones were afforded in acceptable to good yields with high diastereoselectivities.

Rhodium(ii)-catalyzed divergent intramolecular tandem cyclization of N- or O-tethered cyclohexa-2,5-dienones with 1-sulfonyl-1,2,3-triazole: synthesis of cyclopropa[cd]indole and benzofuran derivatives

A novel rhodium(ii)-catalyzed divergent intramolecular tandem cyclization of N- or O-tethered cyclohexa-2,5-dienones and 1-sulfonyl-1,2,3-triazole is disclosed, affording cyclopropa[cd]indole and benzofuran derivatives in moderate to good yields.

Annulation-Induced Cascade Transformation of 5-Iodo-1,2,3-triazoles to 2-(1-Aminoalkyl)benzoxazoles

Base-mediated cyclization of (5-iodo-1,2,3-triazolyl)phenols was proposed as a new synthetic strategy for the in situ generation of diazoimines via electrocyclic ring opening of the fused heterocycle. Cu-catalyzed amination of the intermediate diazoalkanes was employed to develop an efficient cascade approach to functionalized benzoxazoles.

Silver-catalyzed regioselective hydroamination of alkenyl diazoacetates to synthesize γ-amino acid equivalents

A simple protocol to directly access γ-amino acid derivatives by intermolecular regioselective hydroamination of trichloroethyl alkenyldiazoacetates with carbamate using a silver tetrafluoroborate catalyst is described. Density functional theory (DFT) calculations to analyze the reaction mechanism revealed that multiple attractive interactions occur in a transition state to promote the vinylogous addition of nitrogen nucleophiles.

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 imidazole by BF3·Et2O promoted denitrogenative transannulation of N-sulfonyl-1,2,3-triazole

The first BF₃·Et₂O promoted metal-free denitrogenative transannulation of N-sulfonyl-1,2,3-triazole was reported, leading to the synthesis of functionalized imidazoles with a broad scope.

Sulfonation of carbonized xylan-type hemicellulose: a renewable and effective biomass-based biocatalyst for the synthesis of O- and N-heterocycles

The application of biomass-based carbonaceous solid acids in catalysis is attracting increasing attention in the field of chemistry.