Catalytic dehydrogenative cross-coupling: forming carbon-carbon bonds by oxidizing two carbon-hydrogen bonds

Thanks to its unusual stability, metallic gold has been used for thousands of years in jewelry, currency, chinaware, and so forth. However, gold had not become the chemists’ “precious metal” until very recently. In the past few years, reports on gold-catalyzed organic transformations have increased substantially. Thanks to gold-based catalysts, various organic transformations have been accessible under facile conditions with both high yields and chemoselectivity.

Gold-catalyzed organic transformations.

Over the last decade, substantial research has led to the introduction of an impressive number of efficient procedures which allow the selective construction of CC bonds by directly connecting two different CH bonds under oxidative conditions. Common to these methodologies is the generation of the reactive intermediates in situ by activation of both CH bonds. This strategy was introduced by the group of Li as cross-dehydrogenative coupling (CDC) and discloses waste-minimized synthetic alternatives to classic coupling procedures which rely on the use of prefunctionalized starting materials. This Review highlights the recent progress in the field of cross-dehydrogenative C sp 3C formations and provides a comprehensive overview on existing procedures and employed methodologies.

The Cross-Dehydrogenative Coupling of C sp 3H Bonds: A Versatile Strategy for CC Bond Formations

Catalytic transformation of ubiquitous C–H bonds into valuable C–N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C–H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications

C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.

3d Transition Metals for C-H Activation.

A PhI(OAc)(2) mediated selective functionalization of sp(3) C-H bonds adjacent to a nitrogen atom has been reported. When piperidine derivates were used, direct diacetoxylation of alpha and beta sp(3) C-H adjacent to a nitrogen atom were observed to afford various cis-2,3-diacetoxylated piperidines. On the other hand, tetrahydroisoquinoline derivatives gave various alpha-C-H functionalized products in the presence of PhI(OAc)(2). Nitroalkanes, dialkyl malonates, and beta-keto ester are active participants in this coupling reaction. Meanwhile, alpha-amino nitriles can also be obtained by oxidative coupling of amines with malononitrile.

Selective Functionalization of sp3 C−H Bonds Adjacent to Nitrogen Using (Diacetoxyiodo)benzene (DIB)

Enantioselective cross-electrophile reactions remain a challenging subject in metal catalysis, and with respect to data, studies have mainly focused on stereoconvergent reactions of racemic alkyl electrophiles. Here, we report an enantioselective cross-electrophile aryl-alkenylation reaction of unactivated alkenes. This method provides access to a number of biologically important chiral molecules such as dihydrobenzofurans, indolines, and indanes. The incorporated alkenyl group is suitable for further reactions that can lead to an increase in molecular diversity and complexity. The reaction proceeds under mild conditions at room temperature, and an easily accessible chiral pyrox ligand is used to afford products with high enantioselectivity. The synthetic utility of this method is demonstrated by enabling the modification of complex molecules such as peptides, indometacin, and steroids.

Highly Enantioselective Cross-Electrophile Aryl-Alkenylation of Unactivated Alkenes.

A novel copper-catalyzed one-pot functionalization of homopropargylic alcohols that involves trifluoromethylation, aryl migration, and formation of a carbonyl moiety has been developed. This reaction constitutes the first direct conversion of homopropargylic alcohols into CF3-containing 3-butenal or 3-buten-1-one derivatives in a regioselective manner. Mechanistic studies indicate that the 1,4-aryl migration proceeds through a radical pathway.

Copper-Catalyzed One-Pot Trifluoromethylation/Aryl Migration/Carbonyl Formation with Homopropargylic Alcohols

In the last few years, the development of versatile methodologies to incorporate trifluoromethyl groups into organic molecules has attracted significant attention in synthetic chemistry. This review gives an overview over the development on the trifluoromethylation of alkynes, which have not been solely discussed before. Formation of diverse C(sp, sp(2) , sp(3) )-CF3 bonds are all covered in this review.

Recent Developments in the Trifluoromethylation of Alkynes

https://www.rsc.org/suppdata/CC/B9/B923971E/B923971E.PDF

Xue-Yuan Liu

Papers

Selective Functionalization of sp3 C−H Bonds Adjacent to Nitrogen Using (Diacetoxyiodo)benzene (DIB)

Highly Enantioselective Cross-Electrophile Aryl-Alkenylation of Unactivated Alkenes.

Copper-Catalyzed One-Pot Trifluoromethylation/Aryl Migration/Carbonyl Formation with Homopropargylic Alcohols

Recent Developments in the Trifluoromethylation of Alkynes

Preparation of indoles via iron catalyzed direct oxidative coupling.