Efficient synthesis of spirooxindolyl oxazol-2(5H)-ones via palladium(ii)-catalyzed addition of arylboronic acids to nitriles

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.

Selective synthesis of functionalized α,β-multi-substituted α-amino cyclopentanones via an α-iminol rearrangement enabled by Pd-catalyzed addition of arylboronic acids to nitriles

An efficient approach to construct α, β-multi-substituted α-amino cyclopentanones is described through an α-iminol rearrangement enabled by Pd-catalyzed addition of arylboronic acids to nitriles.

Palladium-catalyzed direct construction of oxazoline-containing polycyclic scaffolds via tandem addition/cyclization of nitriles and arylboronic acids

An efficient construction of oxazoline-containing polycyclic scaffolds through a Pd-catalyzed addition/cyclization of (hetero)arene tethered O-acyl cyanohydrin units and arylboronic acids is described.

Palladium(II)-Catalyzed C(sp)–C(sp2) Coupling: A Direct Approach to Multi-Substituted Pyrrolo[1,2-a]pyrazines

A direct synthesis of multi-substituted pyrrolo[1,2-a]pyrazines via palladium(II)-catalyzed C(sp)–C(sp2) cascade coupling and intramolecular cyclization in the presence of ligand was developed. This reaction originates from phenylboronic acids and readily synthesized 2-carbonyl- or 2-formylpyrroloacetonitriles, and affords products in good to excellent yields for a diversity of substrates. Additionally, a possible mechanism for the transformation is proposed.

Transition metal-catalyzed synthesis of spirooxindoles

Spirooxindole is a principal bioactive agent and is observed in several natural products including alkaloids. They are broadly studied in the pharmaceutical field and have a significant role in the evolution of drugs such as anti-viral, anti-cancer, anti-microbial etc. In organic chemistry, an indispensable role is presented by transition metal catalysts. An effective synthetic perspective to spirooxindoles is the use of transition metals as the catalyst. This review discusses the synthesis of spirooxindoles catalyzed by transition metals and covers literature up to 2020.

α-Iminol Rearrangement Triggered by Pd-Catalyzed C-H Addition to Nitriles Sequences: Synthesis of Functionalized α-Amino Cyclopentanones

A α-iminol rearrangement triggered by Pd-catalyzed C-H addition of electronic-rich heteroarenes to cyclobutanone-derived O-acyl cyanohydrins was described, which provided a practical and efficient protocol for the preparation of functionalized α-amino cyclopentanones in an atom- and step-economic fashion. In addition, further synthetic transformations of products have also been demonstrated.

Palladium-catalyzed C-H activation of simple arenes and cascade reaction with nitriles: access to 2,4,5-trisubstituted oxazoles

An efficient and straightforward protocol for the assembly of the pharmaceutically and biologically valuable oxazole skeleton is achieved for the first time from readily available simple arenes and functionalized aliphatic nitriles. This transformation involves palladium-catalyzed C-H activation, carbopalladation and a tandem annulation sequence in one pot. Notably, the reaction proceeds efficiently under redox-neutral conditions, and exhibits high atom-economy. Deuterium-labeling experiments suggested that C-H bond cleavage of the simple arenes might be the rate-determining step.

Palladium-Catalyzed Cascade Reactions of δ-Ketonitriles with Arylboronic Acids: Synthesis of Pyridines

This study presents the first example of the Pd-catalyzed cascade reactions of 5-oxohexanenitrile with arylboronic acids, affording important synthon 2-methylpyridines that can be further translated through C(sp³)-H functionalization to construct pyridine derivatives. Furthermore, this chemistry allows 5-oxo-5-arylpentanenitrile to react with arylboronic acids to provide unsymmetrical 2,6-diarylpyridines. This protocol paves the way for the practical and atom economical syntheses of valuable pyridines with broad functional groups in moderate to excellent yields under mild conditions.

Nickel(ii)-catalyzed C–C, N–C cascade coupling of ketonitriles into substituted pyrroles and pyridines

The first example of nickel complexes as effectively catalyst to C–C, N–C cascade coupling of ketonitriles with arylboronic acids, affording 2,5-diarylpyrroles and 2,6-diarylpyridines.