Ru(II)/Rh(III)-Catalyzed C(sp3)–C(sp3) Bond Formation through C(sp3)–H Activation: Selective Linear Alkylation of 8-Methylquinolines and Ketoximes with Olefins

Rh(III)-Catalyzed C(sp3)-H Thiolation of 8-Methylquinolines Promoted by Benzoic Anhydride

Herein, we developed a ligand-promoted Rh(III)-catalyzed C(sp3)-H thiolation of 8-methylquinolines. The effect of ligands on improving the activity of the catalytic centers has been studied in detail and proven to be significant. Various substituents are well tolerated under this reaction condition to provide potential precursors for organic synthesis. The mechanistic study suggests that the reaction may proceed through a five-membered rhodacycle intermediate via thiolation twice.

Transition-Metal-Catalyzed C-H Bond Activation for the Formation of C-C Bonds in Complex Molecules

Site-predictable and chemoselective C-H bond functionalization reactions offer synthetically powerful strategies for the step-economic diversification of both feedstock and fine chemicals. Many transition-metal-catalyzed methods have emerged for the selective activation and functionalization of C-H bonds. However, challenges of regio- and chemoselectivity have emerged with application to highly complex molecules bearing significant functional group density and diversity. As molecular complexity increases within molecular structures the risks of catalyst intolerance and limited applicability grow with the number of functional groups and potentially Lewis basic heteroatoms. Given the abundance of C-H bonds within highly complex and already diversified molecules such as pharmaceuticals, natural products, and materials, design and selection of reaction conditions and tolerant catalysts has proved critical for successful direct functionalization. As such, innovations within transition-metal-catalyzed C-H bond functionalization for the direct formation of carbon-carbon bonds have been discovered and developed to overcome these challenges and limitations. This review highlights progress made for the direct metal-catalyzed C-C bond forming reactions including alkylation, methylation, arylation, and olefination of C-H bonds within complex targets.

Rh(III)-Catalyzed Alkylation of 8-Methylquinolines with Oxabenzonorbornadienes

Herein, a concise Rh(III)-catalyzed C(sp³)-H alkylation of 8-methylquinolines with oxabenzonorbornadiene scaffolds and other strained olefins has been disclosed. The retention of the oxabenzonorbornadiene skeleton, broad substrate scope, and wide-ranging functional group tolerance are the key features of the developed catalytic methodology. Mechanistic studies revealed that the reaction does not involve a radical pathway, and the five-membered rhodacycle is the key intermediate. This is the first report on the C(sp³)-H alkylation of 8-methylquinolines with strained oxabenzonorbornadiene scaffolds (with ring retention).

Transition-metal-catalyzed C-H bond alkylation using olefins: recent advances and mechanistic aspects

Transition metal catalysis has contributed immensely to C-C bond formation reactions over the last few decades, and alkylation is no exception. The superiority of such methodologies over traditional alkylation is evident from minimal reaction steps, shorter reaction times, and atom economy while also allowing control over regio- and stereo-selectivity. In particular, hydrocarbonation of alkenes has grabbed increased attention due its fundamental ability to effectively and selectively synthesise a wide range of industrially and pharmaceutically relevant moieties. This review attempts to provide a scientific viewpoint and a systematic analysis of the recent developments in transition-metal-catalyzed alkylation of various C-H bonds using simple and activated olefins. The key features and mechanistic studies involved in these transformations are described briefly.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Pd(II)-Catalyzed Arylation/Oxidation of Benzylic C-H of 8-Methylquinolines: Access to 8-Benzoylquinolines

An efficient access to 8-benzoylquinoline was developed by a sequential arylation/oxidation of 8-methylquinolines with aryl iodides in the presence of Pd(OAc)₂. This transformation demonstrates good tolerance of a wide range of functional groups on aryl iodides, providing good to excellent yields of 8-benzoylquinolines.

Rhodium(III)/Chiral Carboxylic Acid Catalyzed Enantioselective C(sp3)-H Alkylation of 8-Ethylquinolines with α,β-Unsaturated Carbonyl Compounds

The enantioselective C-H alkylation of 8-ethylquinolines with enones or acrolein using a Rh^III catalyst and a chiral carboxylic acid is described. Under mild reaction conditions, a binaphthyl-based chiral carboxylic acid enables the enantioselective cleavage of the 8-ethylquinoline C(sp³)-H bond. The obtained results demonstrate the utility of the combination of a high-valent group 9 metal catalyst and a chiral carboxylic acid for the enantioselective C(sp³)-H activation and the subsequent C-C bond formation.