Mn(III)-Mediated Radical Cyclization of o-Alkenyl Aromatic Isocyanides with Boronic Acids: Access to N-Unprotected 2-Aryl-3-cyanoindoles

Photocatalytic cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones for the construction of quinoxalino[2,1-b]quinazolinones

A new kind of building unit, 3-(2-isocyanophenyl)quinazolin-4(3H)-ones, was designed and synthesized for the construction of novel quinoxalino[2,1-b]quinazolinones. The radical cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones with ethers afforded ether-substituted tetracyclic quinoxalino[2,1-b]quinazolinones under photocatalytic and metal-free conditions. In the process, the isocyano accepts a carbon radical to give an imidoyl radical, which adds to the electron-deficient CN bond in quinazolin-4(3H)-one.

Mn(iii)-mediated C-P bond activation of diphosphines: toward a highly emissive phosphahelicene cation scaffold and modulated circularly polarized luminescence

Transition metal mediated C-X (X = H, halogen) bond activation provides an impressive protocol for building polyaromatic hydrocarbons (PAHs) in C-C bond coupling and annulation; however, mimicking both the reaction model and Lewis acid mediator simultaneously in a hetero-PAH system for selective C-P bond cleavage faces unsolved challenges. At present, developing the C-P bond activation protocol of the phosphonic backbone using noble-metal complexes is a predominant passway for the construction of phosphine catalysts and P-center redox-dependent photoelectric semiconductors, but non-noble metal triggered methods are still elusive. Herein, we report Mn(iii)-mediated C-P bond activation and intramolecular cyclization of diphosphines by a redox-directed radical phosphonium process, generating phosphahelicene cations or phosphoniums with nice regioselectivity and substrate universality under mild conditions. Experiments and theoretical calculations revealed the existence of the unusual radical mechanism and electron-deficient character of novel phosphahelicenes. These rigid quaternary bonding skeletons facilitated versatile fluorescence with good tunability and excellent efficiency. Moreover, the enantiomerically enriched crystals of phosphahelicenes emitted intense circularly polarized luminescence (CPL). Notably, the modulated CPL of racemic phosphahelicenes was induced by chiral transmission in the cholesteric mesophase, showing ultrahigh asymmetry factors of CPL (+0.51, -0.48). Our findings provide a new approach for the design of emissive phosphahelicenes towards chiral emitters and synthesized precursors.

Visible Light-Induced Decomposition of Acyl Peroxides Using Isocyanides: Synthesis of Heteroarenes by Radical Cascade Cyclization

Visible light-mediated facile synthesis of heteroarenes, namely, isoquinolines, benzothiazoles, and quinazolines, is demonstrated by employing isocyanides and inexpensive acyl peroxides. It is shown for the first time that singlet-excited isocyanides decompose acyl peroxides into aryl/alkyl radicals. The latter attack isocyanides, yielding imidoyl radicals that subsequently cyclize to afford heteroarene products. The protocol involving radical cascade reactions obviates the requirement of any external photocatalyst, oxidant, additive, and base.

Mn(III)-Mediated Radical Addition/Cyclization of Isocyanides with Aryl Boronic Acids/Diarylphosphine Oxides: Access to 11-Functionalized Dibenzodiazepines

A Mn(III)-mediated radical addition/cyclization reaction of isocyanides with aryl boronic acids/diarylphosphine oxides has been developed. A series of 11-arylated/-phosphorylated dibenzodiazepines were efficiently constructed in moderate to excellent yields under mild reaction conditions via imidoyl radical process. The present protocol offers novel access to functionalized seven-membered N-heterocycles.

Oxidative Radical Transnitrilation of Arylboronic Acids with Trityl Isocyanide

We report a radical transnitrilation of arylboronic acids with trityl isocyanide in the presence of manganese(III) acetate. Many functional groups can be tolerated in this transformation, and a special positive effect of benzoic acid in this reaction has been observed.

Metal-catalyzed reactions of organic nitriles and boronic acids to access diverse functionality

The nitrile or cyano (-CN) group is one of the most appreciated and effective functional groups in organic synthesis, having a polar unsaturated C-N triple bond. Despite sufficient stability and being intrinsically inert, the nitrile group can be easily transformed into many other functional groups, such as amines, carboxylic acids, ketones, etc. which makes it a vital group in organic synthesis. On the other hand, despite several boronic acids having a low level of genotoxicity, they have found wide applicability in the field of organic synthesis, especially in transition metal-catalyzed cross-coupling reactions. Recently, transition-metal-catalyzed cascade additions or addition/cyclization processes of boronic acids to the nitrile group open up exciting and useful strategies to prepare a variety of functional molecules through the formation of C-C, C-N and CO bonds. Boronic acids can be added to the cyano functionality through catalytic carbometallation or through a radical cascade process to provide newer pathways for the rapid construction of various important acyclic ketones or amides, carbamidines, carbocycles and N,O-heterocycles. The present review focuses on various transition-metal-catalyzed additions of boronic acids via carbometallation or radical cascade processes using the cyano group as an acceptor.

Advances in free-radical alkylation and arylation with organoboronic acids

Organoboronic acids act as carbon-centered radical precursors that are widely utilized to construct diverse C-C bonds. This review summarizes the advances in this field. The content is divided into four parts according to the different categories of coupling partners with organoboronic acids. The reaction conditions as well as the mechanisms are demonstrated in each part.

Mn(iii)-Catalyzed cascade cyclization reaction of o-acyl aromatic isocyanides with boronic acids

A Mn(iii)-catalyzed cascade cyclization of o-acyl aromatic isocyanides with boronic acids was examined to give a series of 3-hydroxyindolenines in single-step. This cascade process involved a transmetalation/nucleophilic addition/intramolecular cyclization sequence.

DMF-Assisted Radical Cyclization of o-Isocyanodiaryl Ethers via 1,5-Aryl Migration: Construction of 2-Arylbenzoxazoles

A novel DMF-assisted radical cyclization of o-isocyanodiaryl ethers via 1,5-aryl migration has been developed for the synthesis of a series of 2-arylbenzoxazoles by the FeCl₃/TBHP/Et₃N catalytic system in DMF. However, N,N-dimethylbenzo[d]thiazole-2-carboxamide and N,N-dimethylbenzo[d]selenazole-2-carboxamide were obtained from the corresponding substrate 2-isocyanophenyl p-methoxyphenyl thioether and 2-isocyanodiphenyl selenoether under the same conditions. A possible mechanism may involve aryl 1,5-migration and DMF-assisted radical cyclization of o-isocyanodiaryl ethers.