Copper-Catalyzed Cross Dehydrogenative Coupling Reactions of Tertiary Amines with Ketones or Indoles

α-Vinylation of amides with arylacetylenes: synthesis of allylamines under metal-free conditions

A novel methodology for the α-vinylation of amides with arylacetylenes under metal-free conditions has been introduced. This methodology provides a new protocol to synthesize allylamines. In each product, the amount of the cis-isomer was more than that of the trans-isomer.

Metal-free TEMPO-promoted C(sp³)-H amination to afford multisubstituted benzimidazoles

An efficient TEMPO-air/cat. TEMPO-O2 oxidative protocol was developed to synthesize multisubstituted or fused tetracyclic benzimidazoles via a metal-free oxidative C-N coupling between the sp(3) C-H and free N-H of readily available N(1)-benzyl/alkyl-1,2-phenylenediamines.

Direct approaches to nitriles via highly efficient nitrogenation strategy through C-H or C-C bond cleavage

Because of the importance of nitrogen-containing compounds in chemistry and biology, organic chemists have long focused on the development of novel methodologies for their synthesis. For example, nitrogen-containing compounds show up within functional materials, as top-selling drugs, and as bioactive molecules. To synthesize these compounds in a green and sustainable way, researchers have focused on the direct functionalization of hydrocarbons via C-H or C-C bond cleavage. Although researchers have made significant progress in the direct functionalization of simple hydrocarbons, direct C-N bond formation via C-H or C-C bond cleavage remains challenging, in part because of the unstable character of some N-nucleophiles under oxidative conditions. The nitriles are versatile building blocks and precursors in organic synthesis. Recently, chemists have achieved the direct C-H cyanation with toxic cyanide salts in the presence of stoichiometric metal oxidants. In this Account, we describe recent progress made by our group in nitrile synthesis. C-H or C-C bond cleavage is a key process in our strategy, and azides or DMF serve as the nitrogen source. In these reactions, we successfully realized direct nitrile synthesis using a variety of hydrocarbon groups as nitrile precursors, including methyl, alkenyl, and alkynyl groups. We could carry out C(sp(3))-H functionalization on benzylic, allylic, and propargylic C-H bonds to produce diverse valuable synthetic nitriles. Mild oxidation of C═C double-bonds and C≡C triple-bonds also produced nitriles. The incorporation of nitrogen within the carbon skeleton typically involved the participation of azide reagents. Although some mechanistic details remain unclear, studies of these nitrogenation reactions implicate the involvement of a cation or radical intermediate, and an oxidative rearrangement of azide intermediate produced the nitrile. We also explored environmentally friendly oxidants, such as molecular oxygen, to make our synthetic strategy more attractive. Our direct nitrile synthesis methodologies have potential applications in the synthesis of biologically active molecules and drug candidates.

DDQ-mediated oxidative coupling: an approach to 2,3-dicyanofuran (thiophene)

A facile oxidative coupling of α-carbonyl radicals to 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) for the synthesis of 2,3-dicyanofurans and thiophenes starting from readily available β-diketones, simple ketones, and β-keto thioamides in up to 95% yield in one step was developed. Mechanistic investigations revealed that a radical process could be involved in this transformation, and a water promoted C-C bond cleavage pathway is proposed for the formation of 2,3-dicyanofurans and thiophenes.

Remodeling of fumagillol: discovery of an oxygen-directed oxidative Mannich reaction

An efficient, two-step construction of highly complex alkaloid-like compounds from the natural product fumagillol is described. This approach, which mimics a biosynthetic cyclase/oxidase sequence, allows for rapid and efficient structure elaboration of the basic fumagillol scaffold with a variety of readily available coupling partners. Mechanistic experiments leading to the discovery of an oxygen-directed oxidative Mannich reaction are also described.

Base-promoted dehydrogenative coupling of benzene derivatives with amides or ethers

Electronically neutral and deficient benzene derivatives are introduced into the dehydrogenative coupling as arenes that couple with amides/ethers.

The cross-dehydrogenative coupling of C(sp3)-H bonds: a versatile strategy for C-C bond formations

Over the last decade, substantial research has led to the introduction of an impressive number of efficient procedures which allow the selective construction of CC bonds by directly connecting two different CH bonds under oxidative conditions. Common to these methodologies is the generation of the reactive intermediates in situ by activation of both CH 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 3C formations and provides a comprehensive overview on existing procedures and employed methodologies.

Iron-catalyzed decarboxylative alkenylation of cycloalkanes with arylvinyl carboxylic acids via a radical process

A Fe(acac)₃-catalyzed decarboxylative coupling of 2-(aryl)vinyl carboxylic acids with cycloalkanes was developed by using DTBP as an oxidant through a radical process. This reaction tolerates a wide range of substrates, and products are obtained in good to excellent yields (71–95%). The reaction also shows excellent stereoselectivity, and only trans-isomers are obtained.

FeCl3-catalyzed cascade cyclization in one pot: synthesis of ring-fused tetrahydroquinoline derivatives from arylamines and N-substituted lactams

Multiple cross-dehydrogenative-coupling reactions catalyzed by FeCl3 in one pot were developed. Arylamines and N-substituted lactams were reacted, and ring-fused tetrahydroquinoline derivatives were formed by two C-C bonds and one C-N bond formation as well as one C-N bond cleavage. The lactams were also used as solvent.

Iron-catalyzed oxidative amidation of tertiary amines with aldehydes

Unconventional couple: A new oxidative coupling protocol for amide bond formation has been developed (see scheme). The method provides an efficient and practical route for the synthesis of tertiary amides from readily available tertiary amines and aldehydes in the presence of a simple FeCl(2) catalyst. Mechanistic studies indicated that a peroxide and an iminium ion act as the reactive intermediates in this oxidative amidation.

A fluorescence "turn-on" chemodosimeter for Cu2+ in aqueous solution based on the ion promoted oxidation

We developed a novel method for Cu(2+) detection based on the ion promoted oxidation reaction. Chemodosimeter L (weak fluorescence) can be oxidized into 3-benzothiazoly-7-N,N-diethylaminocoumarin (strong green fluorescence, coumarin 6) by Cu(2+) with high selectivity and sensitivity in HEPES (10 mM, pH = 7.4) buffer containing 50% (v/v) water-CH(3)CN solution.

Recent advances in copper-catalyzed dehydrogenative functionalization via a single electron transfer (SET) process

Copper salts have been developed as versatile catalysts for oxidative coupling reactions in organic synthesis. During these processes, Cu-catalysts are often proposed to serve as a one-electron oxidant to promote the single-electron transfer process. Recently, the transition-metal catalyzed direct dehydrogenative transformation has attracted considerable attention. This tutorial review summarizes the recent advances in the copper-catalyzed dehydrogenative functionalization via a single electron transfer (SET) process achieving C-C, C-N, C-O, C-halogen atoms, C-P, and N-N bond formation.

Visible light-induced oxidative coupling reaction: easy access to Mannich-type products

An efficient methodology for the functionalization of sp(3) C-H bond adjacent to nitrogen has been developed utilizing visible light-induced photoredox catalysis. Through optimization of solvent and light source, the reaction can be rapidly achieved to provide the desired product under mild reaction conditions.

Direct functionalization of (un)protected tetrahydroisoquinoline and isochroman under iron and copper catalysis: two metals, two mechanisms

A highly facile, straightforward synthesis of 1-(3-indolyl)-tetrahydroisoquinolines was developed using either simple copper or iron catalysts. N-protected and unprotected tetrahydroisoquinolines (THIQ) could be used as starting materials. Extension of the substrate scope of the pronucleophile from indoles to pyrroles and electron-rich arenes was realized. Additionally, methoxyphenylation is not limited to THIQ but can be carried out on isochroman as well, again employing iron and copper catalysis.