Heterocyclization of Enediynes Promoted by Sodium Azide: A Case of Ambiguity of X-ray Data and Structure Revision

Domino Aza-Annulations of Enynyl-/(Alkynyl)aryl-acetonitriles to Access Nitrogen-Enriched Heterocycles

Unprecedented domino aza-annulations of (E)-2-en-4-ynyl-acetonitriles (generated from the Morita-Baylis-Hillman acetates of propiolaldehydes for the first time) with sodium azide under metal- and oxidant-free conditions for the assembly of triazolo-pyridines are accomplished. The developed strategy offers broad substrate scope, extending to (2-alkynyl)aryl and indolyl-acetonitriles to provide the corresponding triazolo-fused isoquinolines and β-carbolines, respectively, in good yields. Additionally, the synthetic utility of the products is demonstrated via denitrogenative coupling of fused triazoles with different nucleophiles.

Azides in the Synthesis of Various Heterocycles

In this review, we focus on some interesting and recent examples of various applications of organic azides such as their intermolecular or intramolecular, under thermal, catalyzed, or noncatalyzed reaction conditions. The aforementioned reactions in the aim to prepare basic five-, six-, organometallic heterocyclic-membered systems and/or their fused analogs. This review article also provides a report on the developed methods describing the synthesis of various heterocycles from organic azides, especially those reported in recent papers (till 2020). At the outset, this review groups the synthetic methods of organic azides into different categories. Secondly, the review deals with the functionality of the azido group in chemical reactions. This is followed by a major section on the following: (1) the synthetic tools of various heterocycles from the corresponding organic azides by one-pot domino reaction; (2) the utility of the chosen catalysts in the chemoselectivity favoring C−H and C-N bonds; (3) one-pot procedures (i.e., Ugi four-component reaction); (4) nucleophilic addition, such as Aza-Michael addition; (5) cycloaddition reactions, such as [3+2] cycloaddition; (6) mixed addition/cyclization/oxygen; and (7) insertion reaction of C-H amination. The review also includes the synthetic procedures of fused heterocycles, such as quinazoline derivatives and organometal heterocycles (i.e., phosphorus-, boron- and aluminum-containing heterocycles). Due to many references that have dealt with the reactions of azides in heterocyclic synthesis (currently more than 32,000), we selected according to generality and timeliness. This is considered a recent review that focuses on selected interesting examples of various heterocycles from the mechanistic aspects of organic azides.

V-shaped fluorophores with a 1-methyl-4,5-bis(arylethynyl)imidazole skeleton displaying solid-state fluorescence, acid responsiveness, and remarkable fluorescence solvatochromism

V-Shaped fluorophores with a 1-methyl-4,5-bis(arylethynyl)imidazole skeleton displayed both solid-state and solution fluorescence, which remarkably changed on exposure to acid vapor.

Copper-Catalyzed Multicomponent Domino Reaction of 2-Bromobenzaldehydes, Aryl Methyl Ketones, and Sodium Azide: Access to 1 H-[1,2,3]Triazolo[4,5- c]quinoline Derivatives

A practical copper-catalyzed multicomponent reaction has been developed for the synthesis of 1 H-[1,2,3]triazolo[4,5- c]quinoline derivatives from commercially available 2-bromobenzaldehydes, aryl methyl ketones, and sodium azide. This protocol integrated consecutive base-promoted condensation, [3 + 2] cycloaddition, copper-catalyzed S_NAr, and denitrogenation cyclization sequences. Preliminary mechanistic studies revealed that CuBr₂ acted as a multifunctional catalyst to streamline this domino process. The mild catalytic system enabled effective construction of one C-C and four C-N bonds in one operation.

(Hetero)aromatics from dienynes, enediynes and enyne–allenes

Recent advances in the synthesis of (hetero)aromatics starting from polyenes, such as dienynes, enediynes and enyne–allenes, are discussed.

A highly efficient tandem [3 + 2] “click” cycloaddition/6-exo-cyclization strategy for the construction of triazole fused pyrazines

The pharmaceutically important tetrahydro-[1,2,3]triazolopyrazine heterocyclic architecture has been synthesized via a concise tandem “click”/6-exo-dig cyclization strategy under mild conditions in mixed aqueous–organic media.