Transition-Metal-Free Tandem Cyclization/N-Arylation Reaction: A Method To Access Biaryl Sultam Derivatives via a Diradical Pathway

Radical-mediated chemo-divergent recyclization of 1,2,3,4-benzothiatriazine-1,1-dioxides: alkyl migration and dearomatization

A divergent denitrogenation/recyclization of 1,2,3,4-benzothiatriazine-1,1-dioxides is disclosed, including C(sp2)-alkyl transposition and aniline dearomatization. Regarding the alkyl migration process, a rare radical-mediated model is presented. Synthetically, sterically-congested biaryl sultams and ortho-all carbon quaternary stereocenter-substituted imines are expeditiously assembled in a simple reaction system. Mechanistic insights indicate that an innovative pattern of diradical-triggered addition probably plays an essential role in the process of C(sp2)-alkyl transformation.

Electrochemical Denitrative Cyclization Driven by Alternating Polarity

Alternating current electrolysis has emerged as a promising technique for addressing challenging redox reactions that are otherwise difficult or impossible for direct current electrolysis. Under mild and transition-metal-free reaction conditions, a general electrochemical denitrative cyclization of nitroarenes was developed to access various cyclic sulfone-containing derivatives of biological significance. The key to success lies in the facile manipulation of multiple redox events upon rapid alternating polarity switching to enhance the selectivity and efficiency.

Kobayashi's Aryne Precursor for the One-Step Synthesis of Anthraquinones and Its Application to the Total Synthesis of Chrysophanol, Danthron, and Physcion

A one-step synthetic method to access medicinally essential anthraquinones has been developed by reacting Kobayashi's aryne precursors with 3-sulfonylphthalides following [4 + 2] Hauser-Kraus annulation reaction. The developed method has been implemented for the total synthesis of bioactive natural products, chrysophanol, danthron, and physcion in 30, 20, and 36% overall yields, respectively, from known compounds.

Fluorinated 2,6-Xylenesulfonyl Group: A Protective Group for Amines

We have developed a fluorinated 2,6-xylenesulfonyl group (fluorinated xysyl, ^fXs) as a protective group for amines. The sulfonyl group could be attached to amines by reactions with the corresponding sulfonyl chloride, and survived various conditions, including acidic, basic, and even reductive conditions. The ^fXs group could be cleaved by treatment with a thiolate under mild conditions.

Synthesis of Tritylones via Cascade Reaction of Arynes with 5-Ethoxyoxazoles

A cascade reaction involving arynes and 5-ethoxyoxazoles has been developed toward the synthesis of 9-alkyl/aryl tritylones. 5-Ethoxyoxazoles undergo a [4 + 2] cycloaddition reaction with arynes followed by retro-[4 + 2] cycloaddition, a second intermolecular [4 + 2] cycloaddition reaction, and hydrolytic ring cleavage to generate substituted tritylones in good yields. The conversion of tritylone products to a series of spirocyclic anthrone derivatives has been demonstrated. The reaction is expeditious, exhibits wide scope, and employs readily available starting materials.

Sulfoxylate Anion Radical-Induced Aryl Radical Generation and Intramolecular Arylation for the Synthesis of Biarylsultams

Aryl radical generation from the corresponding aryl halides using an electron donor and subsequent intramolecular cyclization with arenes could be an important advancement in contemporary biaryl synthesis. A green and practically useful synthetic protocol to access diverse six- and seven-membered biarylsultams especially with a free NH group including demonstration of a gram-scale synthesis is reported herein. The sulfoxylate anion radical (SO₂^-•), generated in situ from the reagents rongalite or sodium dithionite (Na₂S₂O₄), was found to be the key single electron transfer agent forming aryl radicals from aryl halides, which upon intramolecular arylation gives biarylsultams with good to excellent yields. The approach features generation of aryl radicals that remained underexplored, use of a cheap and readily available industrial reagents, and transition metal-free, mild, and green reaction conditions.

Tandem aza-Michael addition-vinylogous aldol condensation: synthesis of N-bridged pyridine fused quinolones

Herein, we present a tandem aza-Michael addition-vinylogous aldol condensation strategy for the synthesis of N-bridged pyridine fused quinolone derivatives from quinolones and ynones. The presented tandem transformation features the construction of C-N and CC bonds in a single operation, under transition metal-free conditions. The wide substrate scope and gram scale synthesis of pyridine fused quinolone derivatives expand the synthetic value of the presented protocol.

Organocatalytic synthesis of (Het)biaryl scaffolds via photoinduced intra/intermolecular C(sp2)-H arylation by 2-pyridone derivatives

A unique N,O-bidentate ligand 6-oxo-1,6-dihydro-pyridone-2-carboxylic acid dimethylamide (L1) catalyzed direct C(sp²)-H (intra/intermolecular) arylation of unactivated arenes has been developed to expedite access to (Het)biaryl scaffolds under UV-irradiation at room temperature. The protocol tolerated diverse functional groups and substitution patterns, affording the target products in moderate to excellent yields. Mechanistic investigations were also carried out to better understand the reaction pathway. Furthermore, the synthetic applicability of this unified approach has been showcased via the construction of biologically relevant 4-quinolone, tricyclic lactam and sultam derivatives.

Cobalt-Catalyzed Cyclization of 2-Bromobenzamides with Carbodiimides: A New Route for the Synthesis of 3-(Imino)isoindolin-1-ones

A novel synthetic pathway to approach 3-(imino)isoindolin-1-ones by the Co-catalyzed cyclization reaction of 2-bromobenzamides with carbodiimides has been developed. This catalytic reaction can tolerate a variety of substituents and provide corresponding products in moderate yields for most cases. According to the literature, the reaction mechanism is proposed through the formation of a five-membered aza-cobalacycle complex, which carries out the following reaction subsequence, including nucleophilic addition and substitution, to furnish the desired structures.

Palladium-catalysed cyclisation of ynamides and propargyl tethered iodosulfonamides with boronic acids leading to benzosultams

An efficient and straightforward Pd-catalysed synthesis of diversely substituted sultams utilising ynamides and boronic acids is disclosed; toluene was found to be the most suitable solvent for this transformation. This strategy has been successfully applied to generate dihydrobenzo[d]isothiazole 1,1-dioxides and dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides. The advantages of this protocol are good functional group tolerance, broad substrate scope, high-yielding reaction and low catalyst loading to access benzofused sultams with five-/six-membered rings. The synthetic utility has been demonstrated by a gram-scale synthesis. A plausible catalytic cycle involving carbopalladation has been proposed for this transformation.

Copper-Catalyzed Dual Cyclization for the Synthesis of Quinindolines

A synthetic approach to quinindoline derivatives by the Cu-catalyzed dual cyclization has been developed. This catalytic reaction is a practical method for the systematic synthesis of quinindoline core structure, which contains a limited-step synthetic strategy and can tolerant a wide variety of substituents. In addition, the mechanistic study reveals that the reaction initiates from a Lewis acid accelerated addition of aniline to nitrile and provides the indole substructure, and then the subsequent Cu-catalyzed C-N coupling reaction furnishes the quinoline subunit and affords the quinindoline structure.