Direct C-H arylation of electron-deficient heterocycles with arylboronic acids

Direct alkylation of heteroarenes with unactivated bromoalkanes using photoredox gold catalysis

Although visible light photoredox catalysis has emerged as a powerful tool for the construction of C-C bonds, common catalysts and/or their photoexcited states suffer from low redox potentials, limiting their applicability to alkyl radical generation from substrates with activated carbon-halogen bonds. Radicals derived from these activated compounds, being highly electrophilic or stabilized, do not undergo efficient addition to heteroarenes. Herein we describe the photocatalytic generation of nucleophilic alkyl radicals from unactivated bromoalkanes as part of a universal and efficient cross-coupling strategy for the direct alkylation of heteroarenes using a dimeric gold(i) photoredox catalyst, [Au2(bis(diphenylphosphino)methane)2]Cl2. The method proves to be efficient for alkylation of arenes under mild conditions in the absence of directing groups.

Ag-catalyzed C-H/C-C bond functionalization

Silver, known and utilized since ancient times, is a coinage metal, which has been widely used for various organic transformations in the past few decades. Currently, the silver-catalyzed reaction is one of the frontier areas in organic chemistry, and the progress of research in this field is very rapid. Compared with other transition metals, silver has long been believed to have low catalytic efficiency, and most commonly, it is used as either a cocatalyst or a Lewis acid. Interestingly, the discovery of Ag-catalysis has been significantly improved in recent years. Especially, Ag(i) has been demonstrated as an important and versatile catalyst for a variety of organic transformations. However, so far, there has been no systematic review on Ag-catalyzed C-H/C-C bond functionalization. In this review, we will focus on the development of Ag-catalyzed C-H/C-C bond functionalization and the corresponding mechanism.

Visible light-promoted C–H functionalization of ethers and electron-deficient arenes

Photocatalyst-free visible-light-mediated C–H arylation of ethers via C_(Sp2)–C_(Sp3) C–H functionalization involving hydrogen atom transfer (HAT) pathway.

Palladium-catalyzed direct C–H arylation of pyridine N-oxides with potassium aryl- and heteroaryltrifluoroborates

An efficient ligand-free Pd(OAc)₂-catalyzed selective arylation of pyridine N-oxides using potassium (hetero)aryltrifluoroborates as coupling partners via C–H bond activation was achieved in the presence of TBAI.

Metal free C–H functionalization of diazines and related heteroarenes with organoboron species and its application in the synthesis of a CDK inhibitor, meriolin 1

Here, we report a metal-free cross-coupling reaction of diazines and related heteroarenes with organoboron species.

The medicinal chemist's toolbox for late stage functionalization of drug-like molecules

The advent of modern C–H functionalization chemistries has enabled medicinal chemists to consider a synthetic strategy, late stage functionalization (LSF), which utilizes the C–H bonds of drug leads as points of diversification for generating new analogs.

The microwave-assisted ortho-alkylation of azine N-oxides with N-tosylhydrazones catalyzed by copper(i) iodide

A regioselective direct ortho-alkylation of azine N-oxides has been achieved under ligand-free conditions using copper(i) iodide and microwave conditions.

Synthesis of 8-heteroaryl nitroxoline analogues via one-pot sequential Pd-catalyzed coupling reactions

A series of 8-heteroaryl substituted quinolines were prepared, either by direct C–H arylation of five-membered heteroarenes, or Pd-catalyzed coupling of organoboron reagents with bromoquinolines.

Synthesis and Utility of Dihydropyridine Boronic Esters

When activated by an acylating agent, pyridine boronic esters react with organometallic reagents to form a dihydropyridine boronic ester. This intermediate allows access to a number of valuable substituted pyridine, dihydropyridine, and piperidine products.

Mechanistic Insights into Two-Phase Radical C-H Arylations

Kinetic, spectroscopic, and computational studies of radical C-H arylations highlight the interplay between chemical and physical rate processes in these multiphase reactions. Anomalous concentration dependences observed here may be reconciled by considering the role of phase transfer processes that mediate concentrations in each phase. In addition, understanding interactions through phase boundaries enables their use in optimization of reaction performance.

Recent Advances in the C-H-Functionalization of the Distal Positions in Pyridines and Quinolines

This review summarizes recent developments in the C-H-functionalization of the distal positions of pyridines, quinolines and related azaheterocycles. While the functionalization of the C2 position has been known for a long time and is facilitated by the proximity to N1, regioselective reactions in the distal positions are more difficult to achieve and have only emerged in the last decade. Recent advances in the transition metal-catalyzed distal C-H-functionalization of these synthetically-important azaheterocycles are discussed in detail, with the focus on the scope, site-selectivity and mechanistic aspects of the reactions.

Regioselective Metal-Free Cross-Coupling of Quinoline N-Oxides with Boronic Acids

A novel and operationally simple one-step C-H bond functionalization of quinoline N-oxides to 2-substituted quinolines was developed. This approach enables the regioselective functionalization under external oxidant- and metal-free conditions. The developed transformation represents the first application of the Petasis reaction in functionalization of heterocycles.

Regioselective decarboxylative cross-coupling of carboxy isoquinoline N-oxides

A straightforward method for direct decarboxylative arylation of 1- and 3-carboxy isoquinaldic acid N-oxides with aryl iodides is reported. The reaction proceeded selectively at the carboxy function site to exclusively give the corresponding C-1 or C-3 arylated product. This methodology tolerates various aryl iodides substituted by electronically different groups. Combined with subsequent Reissert-Henze chlorination and SNAr amination, the decarboxylative arylation provides an efficient access to 1,3-functionalized isoquinoline-based antitumor agent.

Structure-activity relationship studies of SEN12333 analogues: determination of the optimal requirements for binding affinities at α7 nAChRs through incorporation of known structural motifs

Alpha7 nicotinic acetylcholine receptors (nAChRs) have implications in the regulation of cognitive processes such as memory and attention and have been identified as a promising therapeutic target for the treatment of the cognitive deficits associated with schizophrenia and Alzheimer's disease (AD). Structure affinity relationship studies of the previously described α7 agonist SEN12333 (8), have resulted in the identification of compound 45, a potent and selective agonist of the α7 nAChR with enhanced affinity and improved physicochemical properties over the parent compound (SEN12333, 8).