Auto-Oxidative Coupling of Glycine Derivatives

N-Arylation of Amino Acid Esters to Expand Side Chain Diversity in Ketoxime Peptide Ligations

Palladium-catalyzed N-arylations of amino acid tert-butyl esters using 4-bromo-N,N-dimethylaniline as a coupling partner are reported. The resulting N-aryl amino acid esters are suitable building blocks for the synthesis of electron-rich N-aryl peptides, which undergo oxidative couplings to aminooxy groups to afford ketoxime peptides under mild conditions. N-aryl amino acid tert-butyl esters possessing unnatural side chains were also accessed via glycine Schiff base alkylation, further increasing the scope of Cα-substitution in ketoxime peptides.

Ketoxime peptide ligations: oxidative couplings of alkoxyamines to N-aryl peptides

Chemoselective ligation methods that preserve or introduce side chain diversity are critical for chemical synthesis of peptides and proteins. Starting from ketone substrates instead of aldehydes in oxime ligation reactions would allow substitution at the site of ligation; however, synthetic challenges to readily access ketone derivatives from common amino acid building blocks have precluded the widespread use of ketoxime peptide ligation reactions thus far. Moreover, ketones are typically much slower to react in condensation reactions compared to aldehydes. Here, one-pot catalyst-free oxidative couplings of α-substituted N-aryl peptides with alkoxyamines provide access to oxime linkages with diverse side chains. Electron-rich N-(p-Me2N-phenyl)-amino acids possessing substituents at the α-carbon were found to be uniquely capable of undergoing site-selective α-C-H oxidations in situ under an O2 atmosphere at neutral pH. Comparative studies with N-arylglycinyl peptides revealed that substitution at the α-carbon caused notable changes in reactivity, with greater sensitivity to solvent and buffer salt composition.

Oxidative [4+2] Cycloaddition of α-(N-Arylamino) Carbonyls with Aryl Alkenes by Multiple C-H Functionalizations and [1,2]-Aryl Shifts

A new, general copper-catalyzed oxidative tandem [4+2] cycloaddition of α-(N-arylamino) carbonyl compounds with aryl alkenes to produce highly substituted quinolines has been developed, which allows the formation of three new C-C bonds through a sequence of multiple C-H functionalizations, annulation, and [1,2]-aryl shifts.

Double-Oxidative Dehydrogenative [4+2]-Cyclization/Dehydrogenation/Oxygenation Tandem Reaction of N-Arylglycine Derivatives with Cumenes

Double-oxidative dehydrogenative (DOD) cyclization is one of the most straightforward strategies for the synthesis of cyclic compounds. A novel approach to substituted 3,4-dihydroquinoline-3-one derivatives via a Cu(II)/DDQ/O₂ system-catalyzed DOD [4+2]-cyclization/dehydrogenation/oxygenation cascade reaction of N-arylglycine derivatives, cumenes, and O₂ has been developed.

Aerobic conversion of benzylic sp3 C–H in diphenylmethanes and benzyl ethers to CO bonds under catalyst-, additive- and light-free conditions

Catalyst-, additive- and light-free aerobic conversion of benzylic C–H to CO bonds is, for the first time, reported.

Iodine monobromide catalysed regioselective synthesis of 3-arylquinolines from α-aminoacetophenones and trans-β-nitrostyrenes

A simple and efficient method for regioselective synthesis of 3-arylquinolines is described from α-aminoacetophenones and trans-β-nitrostyrenes using 20 mol% iodine monobromide as a catalyst in acetonitrile solvent at 80 °C.

Oxidative cross-dehydrogenative [2 + 3] annulation of α-amino ketones with α-keto esters: concise synthesis of clausenamide analogues

A one-pot oxidative cross-dehydrogenative [2 + 3] annulation of α-amino ketones with α-keto esters at room temperature is reported.

Oxone promoted dehydrogenative Povarov cyclization of N-aryl glycine derivatives: an approach towards quinoline fused lactones and lactams

Oxone promoted intramolecular dehydrogenative imino Diels–Alder reaction (Povarov cyclization) of alkyne tethered N-aryl glycine esters and amides has been explored, thus affording biologically significant quinoline fused lactones and lactams.

Recent advances in metal-free aerobic C–H activation

An overview of recent reactions based on the metal-free, dioxygen-induced, C–H activation of various radical precursors.

Molecular Oxygen-Promoted General and Site-Specific Alkylation with Organoboronic Acid

A general alkylating method using organoboronic acid under 1 atm of oxygen is developed. It allows a facile access to a wide range of functionalized molecules with privileged scaffolds in drugs and natural products such as oxindoles, quinolinones, chromones, naphthoquinones, coumarins, and quinolones. In contrast to previous alkylation approaches that generally requiring transition-metal catalysis and a stoichiometric chemical oxidant, the present strategy features metal-free, molecular oxygen as the terminal oxidant and site specificity.

Decarbonylative Formation of Homoallyl Radical Capable of Annulation with N-Arylpropiolamides via Aldehyde Auto-oxidation

A new metal-free aldehyde auto-oxidation strategy that allows the decarbonylative formation of homoallyl radical capable of cascade annulations with alkynes is described. By using various N-arylpropiolamides, the oxidative radical [3 + 2]/[5 + 2] cascade annulation reaction was achieved to produce benzo[ b]cyclopenta[ e]azepin-4(1 H)-ones, which represent a powerful new platform for the intermolecular cycloadditions of alkyne with broad substrate scope and high selectivity.

Oxime Ligation via in situ Oxidation of N-Phenylglycinyl Peptides

Mild conditions for oxime ligations via in situ generation of α-imino amide intermediates are reported. The evaluation of a variety of N-terminal N-phenylglycine residues revealed that a metal-free, chemoselective oxidation was possible using oxygen as the only oxidant in buffer at pH 7.0. Moreover, selective unmasking of an inert residue by addition of potassium ferricyanide is demonstrated. These simple and mild conditions, which can be fine-tuned by the electronic properties of the N-phenylglycine residue, offer unique advantages over conventional approaches for oxime ligations.

Synthesis of α-functionalized α-indol-3-yl carbonyls through direct SN reactions of indol-3-yl α-acyloins

A new and efficient synthesis of α-functionalized α-indol-3-yl ketones from easily available indolyl α-acyloins is reported. This process, catalyzed by Brønsted or Lewis acids, involves an uncommon direct nucleophilic substitution reaction of a secondary α-carbonyl-substituted hydroxyl group. The described methodology allows the introduction of a variety of nucleophiles such as (hetero)arenes, thiophenols, nitroanilines and 1,3-dicarbonyl derivatives. The synthesized α-indol-3-yl carbonyl compounds are important synthetic targets also useful for accessing functionalized tryptophols and furan-3-yl indoles.

Air promoted annulation of thiophenols with alkynes leading to benzothiophenes

Air promoted intermolecular annulation of thiophenols with alkynes, leading to complex benzothiophenes, is reported.

Visible light-induced aerobic oxidative cross-coupling of glycine derivatives with indoles: a facile access to 3,3′ bisindolylmethanes

A rapid synthesis of 3,3′-bisindolylmethanes is achieved via a photocatalyzed double Friedel–Crafts alkylation reaction between glycine derivatives and indoles.

Metal-free photocatalyzed aerobic oxidative Csp3–H functionalization of glycine derivatives: one-step generation of quinoline-fused lactones

This reaction provides facile access to a series of valuable quinoline-fused lactones at room temperature under an air atmosphere.

A copper/O2-mediated direct sp3 C–H/N–H cross-dehydrogen coupling reaction of acylated amines and N-aryl glycine esters

We described a mild and efficient CDC reaction between N-aryl glycine esters and various acylated amines for the synthesis of α-amino α-amide acid esters with an excellent regioselectivity in the presence of copper salts.

Visible light-induced aerobic oxidative cross-coupling of glycine esters with α-angelicalactone: a facile pathway to γ-lactams

A rapid synthesis of substituted γ-lactams is achieved via metal-free photocatalyzed aerobic oxidative dehydrogenative formal [2 + 3] cyclization of glycine esters with α-angelicalactone.

Auto-oxidation promoted sp3 C–H arylation of glycine derivatives

An auto-oxidation promoted sp³ C–H arylation reaction between N-aryl glycine derivatives and electron-rich arenes, leading to the formation of N-aryl α-aryl α-amino acid derivatives, is described. This atom-economical and environmentally benign reaction proceeds smoothly under mild reaction conditions and requires only Brønsted acid and oxygen (balloon). A plausible radical involved mechanism is proposed.

Aerobic oxidative acylation of nitroarenes with arylacetic esters under mild conditions: facile access to diarylketones

A regioselectivet-BuONa-mediated aerobic oxidative acylation of nitroarenes under mild conditions is developed through a cascade CDC/oxidative decarboxylation process.

Visible-light-mediated iodine-catalyzed α-hydroxylation of α-methylene ketones under aerobic conditions

A visible-light-mediated α-hydroxylation of α-methylene ketones using atmospheric oxygen as a green oxidant has been developed with novel substrate selectivity.

CBr4-mediated cross-coupling reactions of α-amino carbonyl compounds with alcohols and thiols to build C–O and C–S bonds, respectively

The direct C(sp³)–H bond functionalization of α-amino carbonyl compounds with CBr₄ to construct C–O and C–S bonds.

One-Pot Synthesis of β-Hydroxysulfones and Its Application in the Preparation of Anticancer Drug Bicalutamide

An efficient one-pot multistep strategy has been developed, comprising auto-oxidative difunctionalization of alkenes, oxidation of sulfides, and a further reduction of peroxides for the synthesis of complex β-hydroxysulfone derivatives from phenthiols and alkenes. This method has several advantageous characteristics, including readily available substrates, low-cost and environmental benign reagents, nontoxic and renewable solvents, and mild reaction conditions. The application of this transformation to the multigram-scale preparation of the anticancer drug bicalutamide is accomplished.

Identifying key intermediates generated in situ from Cu(II) salt-catalyzed C-H functionalization of aromatic amines under illumination

Copper compounds involved in photocatalysis have recently spurred considerable interest for their novel transformations. However, mechanistic investigations are still in infancy. We find a new type of reaction, that is, Cu(II) salt-catalyzed C-H functionalization of aromatic amines triggered by visible light irradiation. An array of mechanistic observations, including high-resolution mass spectrometry, ultraviolet-visible absorption spectrum, electron spin resonance, x-ray absorption near-edge structure, and density functional theory calculation, have identified the key intermediates generated in situ in the transformation. Integration of single-electron transfer, singlet oxygen (¹O₂), and new absorption species, intermediate I and intermediate II formed in situ from Cu(II) salts and substrate amines or imines, respectively, is responsible for the N-H and C-H bond activation of secondary amines to couple with nucleophiles in air, thereby leading to the formation of quinoline, indolo[3,2-c]quinoline, β-amino acid, and 1,4-dihydropyridine derivatives in moderate to good yields under visible light irradiation at room temperature.