Palladium-Catalyzed Site-Selective Benzocylization of Aromatic Acids with o-Fluoro-Substituted Diaryliodonium Salts toward 3,4-Benzocoumarins

A Strongly Ambiphilic Ferrocene-Based Cyclic (Alkyl)(amino)carbene - Specific Decomposition to an Enamine by a 1,2-Phenyl Shift

The recently described crystalline cyclic (alkyl)(amino)carbene with a 1,1'-ferrocenylene (fc) backbone fc(CPh2-C-NMes) (A, Mes=mesityl) is highly reactive due to its particularly pronounced ambiphilicity and is thermally not stable in solution due to an intramolecular insertion of the divalent carbon atom into a methyl C-H bond of the Mes substituent. The closely related congener fc(CPh2-C-N-p-C6H4-tBu) (1) cannot undergo such an insertion reaction. Nevertheless, 1 is too short-lived for isolation due to a rapid 1,2-shift of a phenyl group, furnishing the isomeric cyclic enamine fc[C(Ph)=C(Ph)-N-p-C6H4-tBu] (1') in a specific decomposition process unprecedented for CAACs. Trapping of 1 was possible with carbon monoxide, elemental selenium and with [CuBr(SMe2)], respectively affording the aminoketene 1=C=O, the selenoamide 1=Se and the homoleptic CuI complex [Cu(1)2][CuBr2]. 1 is an even stronger ambiphile than A according to NMR spectroscopic data. Similar to A, 1 does not react with H2, because the experimentally observed intramolecular process is kinetically more favourable according to DFT results.

Base-Promoted One-Pot Strategy for Expeditious Assembly of Highly Functionalized Benzocoumarin Derivatives

A versatile and atom-economic three-component reaction between 3-cyano-4-styrylcoumarins, 1,3-indandione, and aliphatic alcohols is described for synthesizing diversely multifunctionalized benzocoumarins. This strategy allows facile access to various benzocoumarins bearing an amine and a substituted benzoyl scaffold under simple heating conditions. Readily available precursors, operational simplicity, acceptable functional group tolerance, and excellent yields are some highlighted advantages of this transformation.

Additive-Controlled Divergent Synthesis of Fluorenone-4-carboxylic Acids and Diphenic Anhydrides via Rhodium-Catalyzed Oxidative Dimeric Cyclization of Aromatic Acids

A rhodium-catalyzed one-pot access to valuable polycyclic frameworks of fluorenone-4-carboxylic acids and diphenic anhydrides via the oxidative dimeric cyclization of aromatic acids has been developed. This transformation proceeded via carboxyl-assisted 2-fold C-H activation followed by intramolecular Friedel-Crafts or dehydration reactions. The silver salt additive plays a vital role in the chemoselectivity of the products. Diphenic anhydride 3l exhibits a maximum fluorescence quantum yield of up to 59%.

Palladium-Catalyzed Triple Suzuki-Miyaura Reactions Using Cyclic (Vinyl Triflate)iodonium Salts

By using cyclic (vinyl triflate)iodonium salts, a novel triple Suzuki-Miyaura reaction was accomplished for the synthesis of polyaromatic ethylene derivatives in the presence of palladium catalysts. The reaction exhibits extensive compatibility with a wide range of readily available arylboronic acids, giving triaryl-substituted ethylenes in good yields.

Ortho-ester-substituted diaryliodonium salts enabled regioselective arylocyclization of naphthols toward 3,4-benzocoumarins

Cyclic annulation involving diaryliodonium salts is an efficient tool for the construction of two or more chemical bonds in a one-pot process. Ortho-functionalized diaryliodonium salts have showcased distinct reactivity in the exploration of benzocyclization or arylocyclization. With this strategy of ortho-ester-substituted diaryliodonium salts, herein, we utilized a copper catalyst to activate the C-I bond of diaryliodonium salts in the generation of aryl radicals, thus resulting in an annulation reaction with naphthols and substituted phenols. This approach yielded a diverse array of 3,4-benzocoumarin derivatives bearing various substituents.

Diaryliodonium Salts Enabled Arylation, Arylocyclization, and Aryl-Migration

Our research interest focusing on synthetic methodology with diaryliodonium salts, is summarized in this account. Besides employing a dual activation strategy of C-I and ortho C-H bonds, we have introduced vicinal functional groups at ortho-positions of diaryliodonium salts, in which their unique reactivities have been explored in various processes, including arylation, diarylation, cascade annulation, benzocyclization, arylocyclization, and intramolecular aryl migration. The variety of mechanisms of these reactions that involves either transition metals, especially palladium in organometallic catalysis, or transition-metal free conditions, were discussed in the context.

Syntheses of functionalized benzocoumarins by photoredox catalysis

Direct functionalization of inert C(sp³)-H bonds is an attractive synthetic technology for the preparation of pharmaceutically significant compounds in modern synthetic organic chemistry. In this work, we report a new method for the synthesis of functionalized benzocoumarins through the strategy of activation of multiple C-H bonds on 2-aryl toluenes under visible-light-enabled photoredox conditions. This method has the advantages of high functional group compatibility, mild reaction conditions, and effectively avoiding the use of strong oxidants and precious metal catalysts. Detailed mechanistic investigations, including spectroscopic and electrochemical studies, support the reaction's mechanistic course.

Modern metal-catalyzed and organocatalytic methods for synthesis of coumarin derivatives: a review

Coumarin is an important pharmaceutical structural motif, abundantly found in numerous commonly used drugs. Compounds containing this core show a broad spectrum of medicinal properties and biological activities. The increasing importance and wide usages of coumarin derivatives have drawn attention to its synthetic methods, among which metal-catalyzed and organocatalytic methods have proved the most effective. Several metal-catalyzed and/or organocatalytic synthetic strategies for coumarin have been investigated and reported in recent decades. This review focuses on more recent reports on catalysis methods for synthesizing coumarin and coumarin-like structures (including light-mediated methods and nano-catalysts), exploring the mechanistic aspects, simplicity, efficiency, repeatability, and other advantages and disadvantages of these methods.

ortho-Nitro-substituted diaryliodonium salts enabled regioselective cyclization of arylcarboxylic acids toward 3,4-naphthocoumarins

We herein report an efficient regioselective cascade of arylation and cyclization of arylcarboxylic acids via Pd(ii)-activation of both C–I and vicinal C–NO2 bonds of ortho-nitro-substituted diaryliodonium salts.

Palladium Catalyzed Regioselective Cyclization of Arylcarboxylic Acids via Radical Intermediates with Diaryliodonium Salts

Palladium-catalyzed C₂-arylation/intramolecular acylation with arylcarboxylic acids was developed by using diaryliodonium salts. The protocol has the advantage of good step-economy by two chemical bonds formation in one pot.

Base-Catalyzed Intramolecular Defluorination/O-Arylation Reaction for the Synthesis of 3-Fluoro-1,4-oxathiine 4,4-Dioxide

A novel process involving base-catalyzed intramolecular defluorination/O-arylation of readily available α-fluoro-β-one-sulfones was realized and provided a series of 3-fluoro-1,4-oxathiine 4,4-dioxide derivatives in good to excellent yields. Unlike traditional defluorination reactions with stoichiometric base as the deacid reagent, this process is triggered by a catalytic amount of base (TMG: tetramethylguanidine) and molecular sieves serve as both an adsorbent to remove HF acid and an activator to assist C–F bond cleavage.

Palladium-Catalyzed Site-Selective Benzocyclization of Naphthoic Acids with Diaryliodonium Salts: Efficient Access to Benzanthrones

Dual activation of both C-I and vicinal C-H bonds of diaryliodonium salts allowing for diarylation is a subject of rapid construction of π-extended frameworks. Here, we report palladium-catalyzed cascade of C₈-arylation/intramolecular Friedel-Crafts acylation of α-naphthoic acids in the synthesis of benzanthrone derivatives. The step-economical protocol tolerates various substrates, which resulted in a potential molecular library for developing functional polycyclic scaffolds. The approach relies on the synergistic action of strong acid with palladium catalysts to form two bonds in a one-pot procedure.

Rhodium-catalyzed coupling of arenes and fluorinated α-diazo diketones: synthesis of chromones

Rh(iii)-Catalyzed synthesis of chromones using arenes and fluorinated diazo reagents via C–H activation, carbene insertion, and uncatalyzed intramolecular nucleophilic aromatic substitution.