Borinic Acid Catalyzed Regioselective N-Alkylation of Azoles

Regioselective, Lewis Acid-Catalyzed Ring-Openings of 2,3-Aziridyl Alcohols with Azoles

Methods for regioselective ring-opening reactions of N-sulfonyl-protected aziridyl alcohols with azole nucleophiles have been developed. Several classes of azoles, including indazole, substituted pyrazole, benzotriazole, and tetrazole, have been employed as reaction partners, giving rise to C3-selective opening and >3:1 N-selectivity. BF3•OEt2 is the optimal catalyst for most substrate combinations, although examples where diphenylborinic acid (Ph2BOH) provides higher yields, or where the reactions proceed efficiently without a catalyst, are also described. Computational modeling of the BF3•OEt2-catalyzed reaction is consistent with the observed regiochemical outcome. The calculated ring-opening transition state appears to be stabilized by an unconventional OH···FB hydrogen-bonding interaction.

Strategic atom replacement enables regiocontrol in pyrazole alkylation

Pyrazoles are heterocycles commonly found as key substructures in agrochemicals and medicinally active compounds alike1,2. Despite their pervasiveness, established methods fall notably short in delivering complex pyrazoles selectively due to issues of differentiation during either assembly or N-functionalization3. This is a direct consequence of a dominant synthetic strategy that attempts to control selectivity-determining bonds between poorly differentiated starting materials. To overcome this longstanding challenge, we here describe a prototypical example of an alternative conceptual approach, 'strategic atom replacement', in which we synthesize N-alkyl pyrazoles from isothiazoles. The net forward transformation is a 'swap' of the isothiazole sulfur atom with a nitrogen atom and its associated alkyl fragment to deliver the alkylated pyrazole4,5. Linking the two azoles is an orphaned heterocycle class, 1,2,3-thiadiazine-S-oxides, whose synthetic potential has yet to be tapped6. By proceeding through these unusual heterocycles, the typical selectivity and separation challenges associated with exclusively bond-based pyrazole preparations are circumvented, and even minimally differentiated peripheral substituents can be discriminated to afford isomerically pure products.

A Review on Chemistry and Methods of Synthesis of 1,2,4-Triazole Derivatives

This review provides a comprehensive overview of research on 1,2,4-triazoles conducted over the last fifteen years. 1,2,4-Triazoles are highly significant in the pharmaceutical industry, with numerous compounds from this class used clinically as antifungal, antiviral, antibacterial, anti-inflammatory, and antitubercular agents. Beyond their pharmaceutical relevance, this review also explores their role in material science and agriculture. In material science, 1,2,4-triazoles are gaining prominence, particularly in the development of energetic materials (EMs), due to their exceptional properties such as thermal stability, coordination ability, and performance comparable to well-known explosives. Their applications extend to polymers, corrosion inhibitors, and metal-organic frameworks (MOFs), and they play a significant role in the development of functional materials for sensors, catalysis, and energy storage. Additionally, the review addresses general aspects and synthetic methodologies for the functionalization and construction of the 1,2,4-triazole ring. Synthetic methods discussed include metalation synthesis, cyclization of hydrazine derivatives, multicomponent reactions, cyclization of amides and amidines, and microwave-assisted synthesis. Given the significance of the triazole scaffold, its synthesis has garnered considerable attention due to its wide-ranging applications across various industrial sectors.

Al(OTf)3-Catalyzed Regioselective N2-Arylation of Tetrazoles with Diazo Compounds

Regioselective methods to access alkylated tetrazoles still remain a challenging goal. Herein, we describe a novel regioselective protocol for N2-arylation of tetrazoles with diazo compounds using inexpensive Al(OTf)3. This reaction could be conducted under mild conditions to access a diverse array of alkylated tetrazoles with 2-substituted tetrazoles as the major products, demonstrating a comprehensive range of substrate compatibility and excellent functional group compatibility. Mechanistic studies revealed a carbene-free process in this reaction procedure. Furthermore, the scale-up reaction and transformations of the N2-arylation of tetrazole products demonstrated the potential of this strategy.

Boronic Acid-Catalyzed Regio- and Stereoselective N-Glycosylations of Purines and Other Azole Heterocycles: Access to Nucleoside Analogues

In the presence of an arylboronic acid catalyst, azole-type heterocycles, including purines, tetrazoles, triazoles, indazoles, and benzo-fused congeners, undergo regio- and stereoselective N-glycosylations with furanosyl and pyranosyl trichloroacetimidate donors. The protocol, which does not require stoichiometric activators, specialized leaving groups, or drying agents, provides access to nucleoside analogues and enables late-stage N-glycosylation of azole-containing pharmaceutical agents. A mechanism involving simultaneous activation of the glycosyl donor and acceptor by the organoboron catalyst has been proposed, supported by kinetic analysis and computational modeling.

Emergent Organoboron Acid Catalysts

Organoboron acids are stable, organic-soluble Lewis acids with potential application as catalysts for a wide variety of chemical reactions. In this review, we summarize the utility of boronic and borinic acids, as well as boric acid, as catalysts for organic transformations. Typically, the catalytic processes exploit the Lewis acidity of trivalent boron, enabling the reversible formation of a covalent bond with oxygen. Our focus is on recent developments in the catalysis of dehydration, carbonyl condensation, acylation, alkylation, and cycloaddition reactions. We conclude that organoboron acids have a highly favorable prospectus as the source of new catalysts.

Organoboron/Palladium Cocatalytic Allylation of NH-Sulfoximines Using Allylic Alcohols

Synergistic organoboron/palladium cocatalysis enables dehydrative couplings of NH-sulfoximines with allylic alcohols, furnishing the corresponding N-allylated products. The reactions proceed in the absence of a Brønsted base and are tolerant of diverse sulfoximine partners, including functionalized variants. Experimental and computational studies suggest that the sulfoximine reagent is activated by complexation to the boronic acid cocatalyst.

N-Trifluoropropylation of Azoles through N-Vinylation and Sequential Hydrogenation

Installing a fluoroalkyl group onto the nitrogen atom of azoles represents a potential strategy for lead optimization in medicinal chemistry. Herein, we describe a method for the N-trifluoropropylation of azoles. This process is accomplished using a combination of regioselective N-vinylation and sequential hydrogenation. The two-step sequence is applicable to a diverse set of azoles and tolerates a wide range of functionalities. In addition, we showcase its practicability and utility through the gram-scale synthesis and the late-stage modification of a complex molecule.

Silver-Catalyzed Cascade Cyclization of Amino-NH-1,2,3-Triazoles with 2-Alkynylbenzaldehydes: An Access to Pentacyclic Fused Triazoles

An operationally simple Ag(I)-catalyzed approach for the synthesis of isoquinoline and quinazoline fused 1,2,3-triazoles was developed by a condensation and amination cyclization cascade of amino-NH-1,2,3-triazoles with 2-alkynylbenzaldehydes involving three new C-N bond formations in one manipulation, in which the group of -NH of the triazole ring serves as a nucleophile to form the quinazoline skeleton. The efficient protocol can be applied to a variety of substrates containing a range of functional groups, delivering novel pentacyclic fused 1,2,3-triazoles in good-to-excellent yields.

Synergistic Organoboron/Palladium Catalysis for Regioselective N-Allylations of Azoles with Allylic Alcohols

A method for regioselective palladium-catalyzed allylic alkylation of ambident nitrogen heterocycles, employing simple allylic alcohols as electrophile precursors, is described. An organoboron co-catalyst serves both to activate the azole-type nucleophile toward selective N-functionalization and to accelerate the formation of a π-allylpalladium complex from the allylic alcohol. The method can be applied to various heterocycle types, including 1,2,3- and 1,2,4-triazoles, tetrazoles, pyrazoles, and purines, and can be extended to substituted allylic alcohol partners.

Pd-Catalyzed regio- and stereoselective allylic substitution of vinylethylene carbonates with 1,2,4-triazoles

N ¹-Substituted 1,2,4-triazoles are ubiquitous skeletons in medicinal agents, agrochemicals, and organic materials. Herein, an efficient and practical method for the synthesis of N¹-allylated 1,2,4-triazoles via Pd-catalyzed allylic substitution of vinylethylene carbonates (VECs) with 1,2,4-triazoles has been developed. By using a catalyst generated in situ from Pd₂(dba)₃·CHCl₃ and DPPE under mild conditions, the process allows rapid access to N¹-allylated 1,2,4-triazoles bearing diverse functionalities in high yields with excellent N¹-selectivities, linear-selectivities, and Z-stereoselectivities.