Silver-Catalyzed Site-Selective Ring-Opening and C-C Bond Functionalization of Cyclic Amines: Access to Distal Aminoalkyl-Substituted Quinones

Photo- and Cerium-Mediated C─C Bond Cleavage for the Deconstructive Diversification of Cyclic Acids

The selective cleavage of inert carbon-carbon bonds in unstrained rings continues to pose a formidable challenge in chemical synthesis. Current methods for C(sp3) ─C(sp3) bond cleavage are highly limited, typically relying on transition-metal catalysis to facilitate ring-opening via small-ring strain or inducing β-fragmentation after generating radicals from oxygen or nitrogen atoms pre-installed in the substrate. Herein, we introduce an effective strategy for the decarboxylative ring-opening functionalization of α-trisubstituted carboxylic acids, mediated by both light and cerium. This method enables the ring-opening of carboxylic acids with ring sizes ranging from 3 to 12 members, allowing the construction of C─CN, C-halide, C─C, C─Se, and C─oxime bonds. Notably, this reaction does not require the pre-installation of an oxygen atom in the substrate, as the carbonyl group is derived from atmospheric oxygen. Furthermore, late-stage modification establishes distally functionalized carbonyl compounds, which serve as versatile synthons for accessing valuable building blocks.

Selective C-N Bond Cleavage in Unstrained Pyrrolidines Enabled by Lewis Acid and Photoredox Catalysis

Cleavage of inert C-N bonds in unstrained azacycles such as pyrrolidine remains a formidable challenge in synthetic chemistry. To address this, we introduce an effective strategy for the reductive cleavage of the C-N bond in N-benzoyl pyrrolidine, leveraging a combination of Lewis acid and photoredox catalysis. This method involves single-electron transfer to the amide, followed by site-selective cleavage at the C2-N bond. Cyclic voltammetry and NMR studies demonstrated that the Lewis acid is crucial for promoting the single-electron transfer from the photoredox catalyst to the amide carbonyl group. This protocol is widely applicable to various pyrrolidine-containing molecules and enables inert C-N bond cleavage including C-C bond formation via intermolecular radical addition. Furthermore, the current protocol successfully converts pyrrolidines to aziridines, γ-lactones, and tetrahydrofurans, showcasing its potential of the inert C-N bond cleavage for expanding synthetic strategies.

Persulfate promoted carbamoylation of N-arylacrylamides and N-arylcinnamamides with 4-carbamoyl-Hantzsch esters

Carbamoyl-Hantzsch esters were used as carbamoyl radical precursors for oxidative carbamoylation of N-arylacrylamides and N-arylcinnamamides in the presence of inexpensive persulfates. This protocol can be applied to a broad range of substrates with various functional groups, providing a variety of 3,3-disubstituted oxindoles and 3,4-disubstituted dihydroquinolin-2(1H)-ones in moderate to good yields via an intermolecular addition/cyclization process.

Photo- and Metal-Mediated Deconstructive Approaches to Cyclic Aliphatic Amine Diversification

Described herein are studies toward the core modification of cyclic aliphatic amines using either a riboflavin/photo-irradiation approach or Cu(I) and Ag(I) to mediate the process. Structural remodeling of cyclic amines is explored through oxidative C-N and C-C bond cleavage using peroxydisulfate (persulfate) as an oxidant. Ring-opening reactions to access linear aldehydes or carboxylic acids with flavin-derived photocatalysis or Cu salts, respectively, are demonstrated. A complementary ring-opening process mediated by Ag(I) facilitates decarboxylative Csp3-Csp2 coupling in Minisci-type reactions through a key alkyl radical intermediate. Heterocycle interconversion is demonstrated through the transformation of N-acyl cyclic amines to oxazines using Cu(II) oxidation of the alkyl radical. These transformations are investigated by computation to inform the proposed mechanistic pathways. Computational studies indicate that persulfate mediates oxidation of cyclic amines with concomitant reduction of riboflavin. Persulfate is subsequently reduced by formal hydride transfer from the reduced riboflavin catalyst. Oxidation of the cyclic aliphatic amines with a Cu(I) salt is proposed to be initiated by homolysis of the peroxy bond of persulfate followed by α-HAT from the cyclic amine and radical recombination to form an α-sulfate adduct, which is hydrolyzed to the hemiaminal. Investigation of the pathway to form oxazines indicates a kinetic preference for cyclization over more typical elimination pathways to form olefins through Cu(II) oxidation of alkyl radicals.

B(C6 F5 )3 -Catalyzed Regioselective Ring Opening of Cyclic Amines with Hydrosilanes

Opening the ring of cyclic amines by regioselective fission of one of the carbon-nitrogen bonds greatly expands the repertoire of available nitrogen-containing skeletons. Unlike approaches starting from cyclic tertiary amines, methods that can directly open secondary amines are still scarce. The present work discloses an efficient reductive ring opening of either of these cyclic amines using PhSiH₃ under B(C₆ F₅ )₃ catalysis. By this, the direct transformation of unstrained cyclic amines into the corresponding acyclic amines is achieved in a simple one-pot operation. A stepwise mechanism proceeding through the intermediacy of silylammonium ions followed by reductive cleavage of a carbon-nitrogen bond was experimentally verified.

Metal-Free Aminohalogenation of Quinones With Alkylamines and NXS at Room Temperature

A simple and practical strategy for intermolecular aminohalogenation of quinone with alkyl amines and NXS was developed, in which haloamines generated in situ were employed as bifunctional reagents. The reaction system is reliable, efficient and wide in substrate range, which is suitable for the two-fold aminochlorination of 1, 4-benzoquinones, large-scale reaction and late-stage modification of pharmaceuticals.

Menadione: a platform and a target to valuable compounds synthesis

Naphthoquinones are important natural or synthetic compounds belonging to the general class of quinones. Many compounds in this class have become drugs that are on the pharmaceutical market for the treatment of various diseases. A special naphthoquinone derivative is menadione, a synthetic naphthoquinone belonging to the vitamin K group. This compound can be synthesized by different methods and it has a broad range of biological and synthetic applications, which will be highlighted in this review.

Divergent Electrochemical Carboamidation of Cyclic Amines

We developed an electrochemical carboamidation sequence that affords either cyclic β-amidoamine products via direct functionalization or linear hydroxybisamide products via a ring opening pathway. The reaction pathway was dependent on the nature of the N-acyl activating group, with carbamate groups favoring direct isocyanide addition to the N-acyliminium ion intermediate and the benzoyl activating group favoring the ring opening-functionalization pathway. Both protocols are one-pot reaction sequences, have general applicability, and lead to peptide-like products of greatly increased molecular complexity.

Synthesis of N-alkenylisoquinolinones via palladium-catalyzed cyclization/C4–O bond cleavage of oxazolidines

A palladium-catalyzed cascade ring-opening reaction to synthesize N-alkenylisoquinolinones via cyclization and C–O bond cleavage is reported.

Amine hydrochloride salts as bifunctional reagents for the radical aminochlorination of maleimides

Amine hydrochloride salts have been typically used as amination reagents.

B(C6F5)3-catalyzed three-component tandem reaction to construct novel polycyclic quinone derivatives: synthesis of a carbonate salt chromogenic chemosensor

A series novel polycyclic quinone derivatives were constructed providing a carbonate salt chromogenic chemosensor.

The silver catalyzed direct C-H functionalization of quinones with dialkyl amides

DMA and other dialkylamides were successfully used as synthons for the C-H functionalization of quinones. This novel amidoalkylation reaction works with a variety of substituted quinones and dialkyl/alkyl amides, such as DMF, NMP and NMA, and the corresponding products were obtained in moderate to good yields. The amidoalkylation of quinones is demonstrated for the first time. A suitable mechanism and the synthetic utility of these compounds are demonstrated. The molecular docking of compound 5 with an Alzheimer's disease (AD) associated AChE target site was studied.

Deconstructive Oxygenation of Unstrained Cycloalkanamines

A deconstructive oxygenation of unstrained primary cycloalkanamines has been developed for the first time using an auto-oxidative aromatization promoted C(sp³ )-C(sp³ ) bond cleavage strategy. This metal-free method involves the substitution reaction of cycloalkanamines with hydrazonyl chlorides and subsequent auto-oxidative annulation to in situ generate pre-aromatics, followed by N-radical-promoted ring-opening and further oxygenation by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and m-cholorperoxybenzoic acid (mCPBA). Consequently, a series of 1,2,4-triazole-containing acyclic carbonyl compounds were efficiently produced. This protocol features a one-pot operation, mild reaction conditions, high regioselectivity and ring-opening efficiency, broad substrate scope, and is compatible with alkaloids, osamines, and peptides, as well as steroids.

Iron-catalyzed regioselective alkylation of 1,4-quinones and coumarins with functionalized alkyl bromides

A simple and efficient Fe-catalyzed regioselective alkylation of 1,4-quinones and coumarins, using functionalized alkyl bromides as alkylating reagents, has been developed.

Silver-catalyzed oxidative 1,2-alkyletherification of unactivated alkenes with α-bromoalkyl carbonyls: facile access to highly substituted 2,3-dihydrofurans

A silver-catalysed C–Br oxidative functionalization/annulative oxygenation process for producing valuable quaternary-carbon-possessing 2,3-dihydrofuran is presented.