Catalytic Direct Construction of Cyano-tetrazoles

BF3-Mediated C2-Amidation of Quinoline N-Oxides Employing Trifluorodiazoethane and Acetonitrile: Access to 2-N-(Trifluoroethyl)amidoquinolines

A Lewis acid-mediated C2-N-trifluoroethylamidation of quinolines, employing quinoline N-oxides, trifluorodiazoethane, and acetonitrile to forge a new class of N-(quinolin-2-yl)-N-(trifluoroethyl)acetamide is presented in this Letter. The reaction proceeds through a carbene generation/nitrile ylide formation/(3 + 2) cycloaddition/rearrangement cascade to furnish quinoline-2-N-(trifluoroethyl)acetamide derivatives in high yields.

Iron(II) Phthalocyanine-Catalyzed Olefination of Aldehydes with Diazoacetonitrile: A Novel Approach to Construct Alkenyl Nitriles

A novel synthetic approach to preparing alkenyl nitriles via the olefination of aldehydes with diazoacetonitrile catalyzed by iron(II) phthalocyanine in the presence of PPh3 has been developed. A broad variety of aldehydes are efficiently transformed into the corresponding products with the high yields of 75%-97%. And it is also suitable for its gram-scale preparation. The suggested mechanism involves the transformation of the phosphazine to ylide by iron(II) phthalocyanine.

Tetrazole Diversification of Amino Acids and Peptides via Silver-Catalyzed Intermolecular Cycloaddition with Aryldiazonium Salts

Selective structural modification of amino acids and peptides is a central strategy in organic chemistry, chemical biology but also in pharmacology and material science. In this context, the formation of tetrazole rings, known to possess significant therapeutic properties, would expand the chemical space of unnatural amino acids but has received less attention. In this study, we demonstrated that the classic unimolecular Wolff rearrangement of α-amino acid-derived diazoketones could be replaced by a faster intermolecular cycloaddition reaction with aryldiazonium salts under identical practical conditions. This strategy provides an efficient synthetic platform that could transform proteinogenic α-amino acids into a plethora of unprecedented tetrazole-decorated amino acid derivatives with preservation of the stereocenters. Density functional theory studies shed some light on the reaction mechanism and provided information regarding the origins of the chemo- and regioselectivity. Furthermore, this diazo-cycloaddition protocol was applied to construct tetrazole-modified peptidomimetics and drug-like amino acid derivatives.

Additive-free synthesis of fused tricyclic cyanoisoxazolidines using in situ formed cyanonitrones

Herein, we disclose the first report on the generation of cyanonitrone in situ from diazoacetonitrile and nitrosoarene, and its subsequent [3+2] cycloaddition with oxabicyclic alkenes to access fused tricyclic cyanoisoxazolidines. Further, this methodology could be extended to access fused tricyclic trifluoromethylated and phosphonylated isoxazolidines. Surprisingly, the reductive ring-opening of cyanoisoxazolidines was followed by a spontaneous lactonization to produce fused tricyclic amino lactones. Moreover, the N-O bond of the obtained tricyclic trifluoromethylated isoxazolidines could be cleaved to obtain 1,3-amino alcohols.

E3 ligase ligand chemistries: from building blocks to protein degraders

In recent years, proteolysis-targeting chimeras (PROTACs), capable of achieving targeted protein degradation, have proven their great therapeutic potential and usefulness as molecular biology tools. These heterobifunctional compounds are comprised of a protein-targeting ligand, an appropriate linker, and a ligand binding to the E3 ligase of choice. A successful PROTAC induces the formation of a ternary complex, leading to the E3 ligase-mediated ubiquitination of the targeted protein and its proteasomal degradation. In over 20 years since the concept was first demonstrated, the field has grown substantially, mainly due to the advancements in the discovery of non-peptidic E3 ligase ligands. Development of small-molecule E3 binders with favourable physicochemical profiles aided the design of PROTACs, which are known for breaking the rules of established guidelines for discovering small molecules. Synthetic accessibility of the ligands and numerous successful applications led to the prevalent use of cereblon and von Hippel-Lindau as the hijacked E3 ligase. However, the pool of over 600 human E3 ligases is full of untapped potential, which is why expanding the artillery of E3 ligands could contribute to broadening the scope of targeted protein degradation. In this comprehensive review, we focus on the chemistry aspect of the PROTAC design process by providing an overview of liganded E3 ligases, their chemistries, appropriate derivatisation, and synthetic approaches towards their incorporation into heterobifunctional degraders. By covering syntheses of both established and underexploited E3 ligases, this review can serve as a chemistry blueprint for PROTAC researchers during their future ventures into the complex field of targeted protein degradation.

Catalytic regioselective construction of phenylthio- and phenoxyldifluoroalkyl tetrazoles from difluorodiazoketones

Here we report the design and synthesis of two new difluoro-diazoketone reagents (difluorophenylthiol diazoketone and difluorophenoxyl diazoketone) and their [3+2] cycloaddition reactions with aryldiazonium salts under silver catalysis conditions. This protocol enables regioselective access to a broad scope of difluorophenylthiol- and difluorophenoxyl-substituted tetrazole-carbinols in a one-pot operation. Further synthetic derivatizations including dephenylthiolation and unexpected phenylthiol group migration/fluorination allow the efficient preparation of α-difluoromethyl tetrazole-carbinols and α-trifluoromethyl tetrazole-thioethers.

N-Iodosuccinimide-Promoted [3 + 2] Annulation Reaction of Aryldiazonium Salts with Guanidines To Construct Aminotetrazoles

A N-iodosuccinimide (NIS)-promoted [3 + 2] annulation reaction of aryldiazonium salts with guanidines has been developed for the construction of previously elusive 2-aryl-5-amino-2H-tetrazoles. This transformation takes advantage of readily available starting materials, proceeds under metal-free, mild, and robust conditions, and holds broad functional group compatibility. The utility of this protocol is further manifested via coupling, annulation, deamination, and denitrogenation derivatizations.

Cu-Enabled [3 + 2] Annulation of In Situ Formed Nitrile Ylides with Aryldiazonium Salts: Access to 5-Cyano-1,2,4-Triazoles

The unified construction of cyano-substituted 1,2,4-triazoles, particularly the 5-cyano counterparts, remains underdeveloped. Herein we describe a three-component method to access a wide range of 1-aryl 5-cyano-1,2,4-triazoles using readily available 2-diazoacetonitriles, nitriles, and aryldiazonium salts. This regiospecific synthesis relies on the dipolar [3 + 2] annulation of the in situ formed nitrile ylides with aryldiazonium salts. Furthermore, this protocol can be amendable to gram-scale synthesis, chemical transformations of the nitrile moieties, and access to chiral bis(cyano-triazole)-1,1'-naphthalene, which would all be likely applicable in the synthesis of structurally diverse bioactive compounds and novel bidentate ligands for asymmetric catalysis.