The Development of Domino Reactions Incorporating the Heck Reaction: The Formation of N-Heterocycles

Reusable cobalt-copper-catalyzed cross-coupling of (hetero)aryl halides with primary amides under air: investigating a new Co0/CoII-based catalytic cycle

We report an efficient ligand-free cobalt-copper-catalyzed cross-coupling reaction of aryl halides with primary amides and also investigate a new Co0/CoII-based catalytic cycle for this transformation. This reaction successfully couples a wide range of aryl and heteroaryl halides (including chlorides, bromides, and iodides) with various aryl, heteroaryl, and aliphatic primary amides in air under solvent-minimized conditions. This cost-effective method efficiently produces the desired cross-coupling products (N-arylamides) in good to excellent yields, showcasing a broad substrate scope (51 examples) and tolerance to many sensitive functional groups (including heterocycles). This protocol requires no conventional work-up and can be performed without the need for strict inert conditions. The established method is also suitable for gram-scale synthesis. Importantly, the catalyst is environmentally benign, inexpensive, and can be reused several times with insignificant loss of catalytic activity. A series of experiments, including UV spectroscopy, transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and cyclic voltammetry (CV), were carried out to determine the oxidation state of the active catalytic species, and a radical clock experiment using a radical probe was conducted to examine the reaction mechanism. The experiments support the proposed novel mechanism and eliminate the possibility of a radical-based pathway.

C-H functionalization of 2-alkyl tryptamines: direct assembly of azepino[4,5-b]indoles and total synthesis of ngouniensines

The Pictet-Spengler type condensation of tryptamine derivatives and aldehydes or ketones is a classic reaction, and has been previously applied to assemble indole-annulated 5-, 6- and 8-membered heterocyclic rings. In this work, we further expand the synthetic scope of this reaction to the 7-membered azepino[4,5-b]indole skeleton through the direct C-H functionalization of 2-alkyl tryptamines, in which the non-activated methylene group participates in a 7-membered ring formation with aldehydes. By combining this unprecedented ring-forming process with a second C-H olefination at the same carbon, the concise total synthesis of natural products ngouniensines is achieved, demonstrating the synthetic potential of the developed chemistry in simplifying retrosynthetic disconnections.

Recent Advances in Palladium-Catalyzed Asymmetric Heck/Tsuji-Trost Reactions of 1,n-Dienes

Transition-metal catalyzed tandem asymmetric reactions were powerful tools to access various chiral compounds. Many strategies have been developed for the coupling of 1,n-dienes with aryl halides via a tandem Heck/Tsuji-Trost process. However, the control of regio- and stereo-chemistry remains a challenging task. This minireview details the recent advances in the field of asymmetric Heck/Tsuji-Trost reactions catalyzed by palladium complex, which have opened new opportunities and expanded our understanding in this area of research in recent years.

A PPh3-catalyzed sequential annulation reaction to construct cyclopentane-fused dihydropyrazolone-pyrrolidinediones

A PPh3-catalyzed sequential cycloaddition of maleimides with unsaturated pyrazolones has been developed. This protocol provides a simple and practical strategy for the construction of dispirocyclopentyl-[dihydropyrazolone-pyrrolidinedione] pyrrolidinedione skeletons containing five contiguous stereogenic centers, including two spiro-quaternary centers, with moderate yields (34-73%) and excellent diastereoselectivities (>20 : 1).

A One-Pot Synthesis of Oxazepine-Quinazolinone bis-Heterocyclic Scaffolds via Isocyanide-Based Three-Component Reactions

A novel, efficient and environmentally friendly approach has been developed for the synthesis of biologically important bis-heterocyclic oxazepine-quinazolinone derivatives. The structurally interesting compounds of high purity were synthesized by a one-pot three-component reaction of 2-(2-formylphenoxy) acetic acid and 2-aminobenzamide as bifunctional reagents and an isocyanide without using any catalyst, with excellent overall yields.

Pd-catalyzed intramolecular C-N bond cleavage, 1,4-migration, sp3 C-H activation, and Heck reaction: four controllable diverse pathways depending on the judicious choice of the base and ligand

Diverse and controllable pathways induced by palladium-catalyzed intramolecular Heck reaction of N-vinylacetamides for the synthesis of nitrogen-containing products in reasonable to high yields via tuning the phosphine ligands and bases are reported. Domino reactions including unique β-N-Pd elimination, 1,4-Pd migration, or direct acyl C-H bond functionalization were found to be involved forming different products, respectively. Given the ability of using the same starting material to generate diverse products via completely different chemoselective processes, these current methodologies offer straightforward access to valuable nitrogen-containing products under mild reaction conditions as well as inspire the discovery of novel reactions.

Sequential hydroformylation/diels-alder processes: one-pot synthesis of polysubstituted cyclohexenes, cyclohexadienes, and phthalates from alkynes

A novel, one-pot hydroformylation/Diels-Alder sequence for the synthesis of multisubstituted cyclohexenes, cyclohexadienes, and phthalates has been developed. Various alkynes were efficiently converted into the corresponding products in good yields and with excellent diastereoselectivity through palladium-catalyzed hydroformylation followed by an AAD-type reaction (AAD: Amides-Aldehydes-Dienophiles). In view of the availability of the substrates, the atom-efficiency of the overall process, and the convenient introduction of substituents in the cyclohexene ring, this method complements current methods for the preparation of polysubstituted cyclohexane derivatives.

Pharmacological importance of optically active tetrahydro-β-carbolines and synthetic approaches to create the C1 stereocenter

1,2,3,4-Tetrahydro-β-carbolines (THβCs) are a pharmacologically important group of compounds belonging to the indole alkaloids. C1-Substituted optically active THβCs have been the target of extensive synthetic efforts due to the presence of the scaffold in numerous natural products and synthetic targets. This review briefly summarizes the methods to obtain the C1 stereocenter and concentrates on evaluating the pharmacological importance of optically active C1-substituted THβCs, including their PDE5-inhibitory, antimalarial, antiviral and antitumor activities.

A convenient palladium-catalyzed carbonylative synthesis of quinazolines from 2-aminobenzylamine and aryl bromides

An interesting approach for the synthesis of 2-functionalized quinazolines has been developed. Various quinazolines have been produced in moderate to excellent yields.

2-(4-Methyl-phen-yl)-3-oxo-4-phenyl-2,3,3a,4,9,9a-hexa-hydro-1H-benzo[f]iso-indole-6-carbo-nitrile

In the title compound, C₂₆H₂₂N₂O, one phenyl ring, one five-membered N-heterocyclic ring and one six-membered carbocyclic ring make up the hexa­hydro­benzo[f]iso­indole core. Another phenyl group is attached to the heterocyclic N atom as a substituent. The non-aromatic five- and six-membered rings both exhibit boat conformations. In the crystal, weak C—H⋯O and C—H⋯N inter­actions establish the observed three-dimensional structure. The crystal studied was refined as an inversion twin.

4-(6-Benzyl-7-oxo-1,2,3,4,5,5a,5a1,6,7,7a,8,12b-dodecahydrobenzo[f]cycloocta[cd]isoindol-8-yl)benzonitrile

In the title compound, C₃₁H₃₀N₂O, the cis-fused cyclo­hexene and cyclo­octane rings adopt boat and boat-chair conformations, respectively. The essentially planar five-membered N-heterocyclic ring [r.m.s. deviation = 0.017 (1) Å] is cis- and trans-fused, respectively, with the cyclo­hexene and cyclo­octane rings. In the crystal, mol­ecules are linked into inversion dimers through pairs of weak C—H⋯O inter­actions.

4-(4-Fluoro-benzo-yl)-3-phenyl-3,4-di-hydro-naphthalen-1(2H)-one

In the title compound, C₂₃H₁₇FO₂, the cyclo­hexenone ring has an envelope conformation, the flap atom being the C atom to which the phenyl ring is attached. The 4-fluoro­benzoyl ring and the phenyl ring are inclined to one another by 28.77 (7)°, and by 52.00 (7) and 44.77 (7) °, respectively, to the aromatic ring fused to the cyclo­hexenone ring. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming a two-dimensional network lying parallel to (100).