Fused Polycyclic Compounds via Cycloaddition of 4-(1′-Cyclohexenyl)-5-iodo-1,2,3-triazoles with 4-Phenyl-1,2,4-triazoline-3,5-dione: The Importance of a Sacrificial Iodide Leaving Group

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.

Chemoselective Modification of Vinyl DNA by Triazolinediones

A new method for the post-synthetic modification of nucleic acids was developed that involves mixing a phenyl triazolinedione (PTAD) derivative with DNA containing a vinyl nucleobase. The resulting reactions proceeded through step-wise mechanisms, giving either a formal [4+2] cycloaddition product, or, depending on the context of nucleobase, PTAD addition along with solvent trapping to give a secondary alcohol in water. Catalyst-free addition between PTAD and the terminal alkene of 5-vinyl-2'-deoxyuridine (VdU) was exceptionally fast, with a second-order rate constant of 2×10³  m^-1  s^-1 . PTAD derivatives selectively reacted with VdU-containing oligonucleotides in a conformation-selective manner, with higher yields observed for G-quadruplex versus duplex DNA. These results demonstrate a new strategy for copper-free bioconjugation of DNA that can potentially be used to probe nucleic acid conformations in cells.

Mechanism of Copper(I)-Catalyzed 5-Iodo-1,2,3-triazole Formation from Azide and Terminal Alkyne

5-Iodo-1,2,3-triazole (iodotriazole) can be prepared from a copper(I)-catalyzed reaction between azide and terminal alkyne in the presence of an iodinating agent, with 5-protio-1,2,3-triazole (protiotriazole) as the side product. The increasing utilities of iodotriazoles in synthetic and supramolecular chemistry drive the efforts in improving their selective syntheses based on a sound mechanistic understanding. A routinely proposed mechanism takes the cue from the copper(I)-catalyzed azide-alkyne cycloaddition, which includes copper(I) acetylide and triazolide as the early and the late intermediates, respectively. Instead of being protonated to afford protiotriazole, an iodinating agent presumably intercepts the copper(I) triazolide to give iodotriazole. The current work shows that copper(I) triazolide can be iodinated to afford iodotriazoles. However, when the reaction starts from a terminal alkyne as under the practical circumstances, 1-iodoalkyne (iodoalkyne) is an intermediate while copper(I) triazolide is bypassed on the reaction coordinate. The production of protiotriazole commences after almost all of the iodoalkyne is consumed. Using (1)H NMR to follow a homogeneous iodotriazole forming reaction, the rapid formation of an iodoalkyne is shown to dictate the selectivity of an iodotriazole over a protiotriazole. To ensure the exclusive production of iodotriazole, the complete conversion of an alkyne to an iodoalkyne has to, and can be, achieved at the early stage of the reaction.

Energetic derivatives of 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole

This study presents the preparation of the novel nitrogen-rich compound 5-(5-amino-2H-1,2,3-triazol-4-yl)-1H-tetrazole (5) in a five step synthesis, and additionally its more energetic derivatives with azido (6) and nitro (7) groups, as well as a diazene bridge (8).

Ruthenium-catalyzed cycloadditions of 1-haloalkynes with nitrile oxides and organic azides: synthesis of 4-haloisoxazoles and 5-halotriazoles

(Cyclopentadienyl)(cyclooctadiene) ruthenium(II) chloride [CpRuCl(cod)] catalyzes the reaction between nitrile oxides and electronically deficient 1-choro-, 1-bromo-, and 1-iodoalkynes leading to 4-haloisoxazoles. Organic azides are also suitable 1,3-dipoles, resulting in 5-halo-1,2,3-triazoles. These air-tolerant reactions can be performed at room temperature with 1.25 equivalents of the respective 1,3-dipole relative to the alkyne component. Reactive 1-haloalkynes include propiolic amides, esters, ketones, and phosphonates. Post-functionalization of the halogenated azole products can be accomplished by using palladium-catalyzed cross-coupling reactions and by manipulation of reactive amide groups. The lack of catalysis observed with [Cp*RuCl(cod)] (Cp* = pentamethylcyclopentadienyl) is attributed to steric demands of the Cp* (η(5)-C5Me5) ligand in comparison to the parent Cp (η(5)-C5H5). This hypothesis is supported by the poor reactivity of [(η(5)-C5Me4CF3)RuCl(cod)], which serves as a an isosteric mimic of Cp* and as an isoelectronic analogue of Cp.