Copper(II)-Catalyzed Monoarylation of Vicinal Diols with Diaryliodonium Salts

A Modular Dual-Catalytic Aryl-Chlorination of Alkenes

Alkyl chlorides are a class of versatile building blocks widely used to generate C(sp3)-rich scaffolds through transformation such as nucleophilic substitution, radical addition reactions and metal-catalyzed cross-coupling processes. Despite their utility in the synthesis of high-value functional molecules, distinct methods for the preparation of alkyl chlorides are underrepresented. Here, we report a visible-light-mediated dual catalysis strategy for the modular synthesis of highly functionalized and structurally diverse arylated chloroalkanes via the coupling of diaryliodonium salts, alkenes and potassium chloride. A distinctive aspect of this transformation is a ligand-design-driven approach for the development of a copper(II)-based atom-transfer catalyst that enables the aryl-chlorination of electron-poor alkenes, complementing its iron(III)-based counterpart that accommodates non-activated aliphatic alkenes and styrene derivatives. The complementarity of the two dual catalytic systems allows the efficient aryl-chlorination of alkenes bearing different stereo-electronic properties and a broad range of functional groups, maximizing the structural diversity of the 1-aryl, 2-chloroalkane products.

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Catalytic Approaches to Chemo- and Site-Selective Transformation of Carbohydrates

Carbohydrates are a fundamental unit playing pivotal roles in all the biological processes. It is thus essential to develop methods for synthesizing, functionalizing, and manipulating carbohydrates for further understanding of their functions and the creation of sugar-based functional materials. It is, however, not trivial to develop such methods, since carbohydrates are densely decorated with polar and similarly reactive hydroxy groups in a stereodefined manner. New approaches to chemo- and site-selective transformations of carbohydrates are, therefore, of great significance for revolutionizing sugar chemistry to enable easier access to sugars of interest. This review begins with a brief overview of the innate reactivity of hydroxy groups of carbohydrates. It is followed by discussions about catalytic approaches to enhance, override, or be orthogonal to the innate reactivity for the transformation of carbohydrates. This review avoids making a list of chemo- and site-selective reactions, but rather focuses on summarizing the concept behind each reported transformation. The literature references were sorted into sections based on the underlying ideas of the catalytic approaches, which we hope will help readers have a better sense of the current state of chemistry and develop innovative ideas for the field.

Copper-Catalyzed C–H Arylation of Fused-Pyrimidinone Derivatives Using Diaryliodonium Salts

Copper-catalyzed Csp2–Csp2 bond forming reactions through C–H activation are still one of the most useful strategies for the diversification of heterocyclic moieties using various coupling partners. A catalytic protocol for the C–H (hetero)arylation of thiazolo[5,4-f]quinazolin-9(8H)-ones and more generally fused-pyrimidinones using catalyst loading of CuI with diaryliodonium triflates as aryl source under microwave irradiation has been disclosed. The selectivity of the transfer of the aryl group was also disclosed in the case of unsymmetrical diaryliodonium salts. Specific phenylation of valuable fused-pyrimidinones including quinazolinone are provided. This strategy enables a rapid access to an array of various (hetero)arylated N-containing polyheteroaromatics as new potential bioactive compounds.

Metal-free regioselective formation of C-N and C-O bonds with the utilization of diaryliodonium salts in water: facile synthesis of N-arylquinolones and aryloxyquinolines

Regioselective construction of crucial C-N and C-O bonds leading to N-arylquinolones and aryloxyquinolines has been accomplished by employing easily accessible diaryliodonium salts and quinolones in water under metal- and ligand-free conditions. This operationally simple strategy is significant due to mild reaction conditions, high product yields, recyclability of released iodoarenes and scalability to the gram level. The practical utility of the developed protocol was proved by the arylation of medicinally important heterocycles like acridin-9(10H)-one, 3-methylquinoxalin-2(1H)-one and 1H-benzo[d]imidazol-2(3H)-one.

Competing Pathways in O-Arylations with Diaryliodonium Salts: Mechanistic Insights

A mechanistic study of arylations of aliphatic alcohols and hydroxide with diaryliodonium salts, to give alkyl aryl ethers and diaryl ethers, has been performed using experimental techniques and DFT calculations. Aryne intermediates have been trapped, and additives to avoid by-product formation originating from arynes have been found. An alcohol oxidation pathway was observed in parallel to arylation; this is suggested to proceed by an intramolecular mechanism. Product formation pathways via ligand coupling and arynes have been compared, and 4-coordinated transition states were found to be favored in reactions with alcohols. Furthermore, a novel, direct nucleophilic substitution pathway has been identified in reactions with electron-deficient diaryliodonium salts.

The protecting-group free selective 3'-functionalization of nucleosides

The direct and chemoselective 3'-phosphoramidation, phosphorylation and acylation of nucleosides are described. Upon the discovery of a novel 3'-phosphorylamidation of therapeutic nucleoside analogues with DBU, we explored the mechanism of this rare selectivity through a combination of NMR spectroscopy and computational studies. The NMR and computational findings allowed us to develop a predictive computational model that accurately assesses the potential for 3'-functionalization for a broad range of nucleosides and nucleoside mimetics. The synthetic utility of this model was exemplified by demonstration on a broad scope of nucleosides and electrophiles yielding targets that were previously only accessible via a protection/deprotection sequence or an enzymatic approach.

Synthesis of Functionalized Dihydrobenzofurans by Direct Aryl C-O Bond Formation under Mild Conditions

A method for the synthesis of dihydrobenzofurans by a direct aryl C-O bond formation is described. A mechanistic pathway for the reaction, distinct from previously described similar transformations, allows for mild reaction conditions that are expected to be compatible with functionalized substrates.

Copper-Catalyzed N-Arylation of 2-Pyridones Employing Diaryliodonium Salts at Room Temperature

A new and mild synthetic approach for the N-arylation of 2-pyridones with diaryliodonium salts has been developed. Most reactions proceed readily at room temperature in the presence of 10 mol % of copper chloride. As a result, a wide range of N-arylpyridine-2-ones were synthesized in yields of 23% to 99%. With this method, an antifibrotic drug, Pirfenidone, was successfully synthesized in 99% yield within 30 min at room temperature.

Transition metal-free N-arylation of secondary amides through iodonium salts as aryne precursors

A transition metal-free approach for N-arylation of secondary amides was developed via diaryliodonium salts as aryne precursors.

Arylation with Diaryliodonium Salts

This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-λ3-iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed.

Recognition and site-selective transformation of monosaccharides by using copper(II) catalysis

We demonstrate copper(II)-catalyzed acylation and tosylation of monosaccharides. Various carbohydrate derivatives, including glucopyranosides and ribofuranosides, are obtained in high yields and regioselectivities. Using this versatile strategy, the site of acylation can be switched by choice of ligand. Preliminary mechanistic studies support nucleophilic addition of a copper-sugar complex to the acyl chloride to be turnover limiting.