New Entry to the Synthesis of α-Iminonitriles by Lewis Acid Mediated Isomerization of Cyano-Substituted Iminoisobenzofurans Prepared by Palladium-Catalyzed Three-Component Coupling of Arynes, Isocyanides, and Cyanoformates

Study on the ArI-catalyzed intramolecular oxy-cyclization of 2-alkenylbenzamides to benzoiminolactones

A new intramolecular oxy-cyclization of 2-alkenylbenzamides catalyzed by ArI has been developed. This protocol is highlighted by its metal-free catalytic system and extremely short reaction time, providing efficient and straightforward access to various benzoiminolactones in good to excellent yields. Interestingly, a regioselective transformation occurred when using two different reaction systems. Mechanistic studies suggested that mCPBA acts as both oxidant and ligand at the IIII center, and the Lewis acid BF3 accelerated ligand exchange and reductive elimination in the catalytic process.

Visible-light-induced intramolecular sp3 C-H oxidation of 2-alkyl-substituted benzamides for the synthesis of functionalized iminoisobenzofurans

We have developed a protocol for the synthesis of functionalized iminoisobenzofurans by means of visible-light-induced intramolecular cyclization reactions of 2-alkyl-substituted benzamides. This one step-economical protocol, which involves intramolecular sp3 C-O bond formation, features mild reaction conditions, exclusive chemoselectivity, and high yields.

Synthesis of Imides, Imidates, Amidines, and Amides by Intercepting the Aryne-Isocyanide Adduct with Weak Nucleophiles

New aryne-based multicomponent coupling reactions for the formation of functionalized aromatic compounds have been developed. Arynes generated from triynes or tetraynes through the hexadehydro Diels-Alder reaction readily react with isocyanide to generate nitrilium intermediate. Intercepting this nitrilium species with various weak nucleophile including carboxylic acids, alcohols, sulfonamides, or water generated the corresponding imides, imidates, amidines, or amides. The high regioselectivity of these transformations was mainly controlled by the substituents of the arynes.

Arynes and isocyanides: Two close-knit partners in multicomponent reactions

Despite benzyne has been known since 1940, this fascinating species has received much attention only over the last decades. The renaissance of interest in aryne chemistry is ascribable to the seminal discovery that arynes can be generated in situ from stable and commercially available precursors under mild and neutral conditions. Thanks to their high reactivity, arynes are key intermediates in countless chemical transformations ranging from cycloadditions to insertions and, among all these approaches, multicomponent reactions (MCRs) are currently standing out in this field. In particular, this short article is focused on MCRs involving the concomitant use of benzyne and isocyanides. Furthermore, the first overview on aryne MCRs triggered by α-isocyanoacetamides is presented.

Cyanide-Free Ce(III)-Catalyzed Highly Efficient Synthesis of α-Iminonitriles from 2-Aminopyridines and Nitroalkenes via Intermolecular Dehydration Reaction

A direct and rapid method for the synthesis of α-iminonitriles achieved good to excellent yields. A novel intermolecular dehydration reaction between 2-aminopyridines and nitroalkenes is reported via a rare-earth-metal catalyst. The merits of this transformation include cyanide-free protocol, short reaction time, simple operation, water as the only byproduct, commercially available reagents, good functional group tolerance, etc. Moreover, nitroalkenes are demonstrated as a new "CN" source in this transformation.

Employing carboxylic acids in aryne multicomponent coupling triggered by aziridines/azetidines

The transition-metal-free aryne multicomponent coupling (MCC) involving carboxylic acids initiated by aziridines/azetidines leading to the synthesis of N-aryl β/γ-amino alcohol derivatives has been developed.

Synthesis of Phenolic Compounds by Trapping Arynes with a Hydroxy Surrogate

Trapping of arynes with various nucleophiles provides a range of heteroatom-functionalized arene derivatives, but the corresponding reaction with water does not provide phenol derivatives. Silver trifluroacetate (AgO₂CCF₃) can nicely solve this problem. It was found that in typical organic solvent, AgO₂CCF₃ readily reacts with arynes to generate trifluoroacetoxy organosilver arene intermediate, which, upon treating with silica gel, provides phenolic products. This protocol can be extended to the synthesis of α-halofunctionalized phenol derivatives by simply adding NBS (N-bromosuccinimides) or NIS (N-iodosuccinimides) to the reaction along with silver trifluroacetate, which provided α-bromo or α-iodophenol derivatives in good yield. However, the similar reactions with NCS (N-chlorosuccinimides) afforded only the protonated product instead of the expected α-chlorophenols derivatives. Interestingly, substrates containing silyl substituents on 1,3-diynes resulted in α-halotrifluoroacetates rather than their hydrolyzed product. Additionally, trapping the same arynes with other oxygen-based nucleophiles containing silver counter cation, along with NXS (N-halosuccinimides), generated α-halooxyfunctionalized products.

Synthesis of Oxygen Heterocycles via Aromatic C-O Bond Formation Using Arynes

Most of the synthetic approaches to the benzo-fused heterocycles containing an oxygen atom have involved the use of phenol derivatives as a starting material. This review highlights the new synthetic approaches involving the aromatic C-O bond-forming process using arynes. The insertion of arynes into the C=O bond gives the unstable intermediates, [2 + 2] cycloaddition-type adducts, which can be easily converted into a variety of oxygen atom-containing heterocycles in a single operation. In this review, the syntheses of oxygen heterocycles, such as coumarin, chromene, xanthene, dihydrobenzofuran and benzofuran derivatives, via the insertion of arynes into the C=O bond of aldehydes or formamides are summarized.

Pd-catalyzed three-component coupling of terminal alkynes, arynes, and vinyl cyclopropane dicarboxylate

A palladium-catalyzed three-component coupling involving in situ generated arynes, terminal alkynes, and vinyl cyclopropane dicarboxylate has been developed. The process demonstrates the first example of aryne chemistry combined with the ring opening of vinyl cyclopropanes. This efficient method using readily available starting materials generates two new carbon-carbon bonds in one pot.