151-10-0Relevant articles and documents
Enantioselective total synthesis of (-)-blennolide A
Tietze, Lutz F.,Ma, Ling,Reiner, Johannes R.,Jackenkroll, Stefan,Heidemann, Sven
, p. 8610 - 8614 (2013)
Blennolide A can be synthesized through an enantioselective domino-Wacker/carbonylation/methoxylation reaction of 7 a with 96 % ee and an enantioselective Wacker oxidation of 7 b with 89 % ee. Further transformations led to the α,β-unsaturated ester (E)-17, which was subjected to a highly selective Michael addition, introducing a methyl group to give 18 a. After a threefold oxidation and an intramolecular acylation, the tetrahydroxanthenone 4 was obtained, which could be transformed into (-)-blennolide A (ent-1) in a few steps. Domino effect: An enantioselective domino-Wacker/carbonylation/methoxylation process and an enantioselective Wacker oxidation are the key steps in the first total synthesis of the fungal metabolite blennolide A (see scheme). Copyright
Facile C-S Bond Cleavage of Aryl Sulfoxides Promoted by Bronsted Acid
Brutiu, Bogdan R.,Klose, Immo,Maulide, Nuno
, p. 488 - 490 (2021)
A method for the Bronsted acid promoted desulfination of aryl sulfoxides is presented. In the presence of a thiol, electron-rich sulfoxides undergo C-S bond cleavage to give the corresponding protodesulfinated arenes and disulfides.
Carbon Kinetic Isotope Effects and the Mechanisms of Acid-Catalyzed Decarboxylation of 2,4-Dimethoxybenzoic Acid and CO2 Incorporation into 1,3-Dimethoxybenzene
Vandersteen, Adelle A.,Howe, Graeme W.,Sherwood Lollar, Barbara,Kluger, Ronald
, p. 15049 - 15053 (2017)
The rate of decarboxylation of 2,4-dimethoxybenzoic acid (1) is accelerated in parallel to the extent that the carboxyl group acquires a second proton (1H+). However, the conjugate acid would resist C-C bond breaking as that would lead to formation of doubly protonated CO2. An alternative via formation of a higher-energy protonated phenyl tautomer (2H+) prior to C-C bond breaking would produce protonated CO2, an energetically inaccessible species that can be avoided by transfer of the carboxyl proton to water in the same step. Headspace sampling of CO2 that evolves in the acid-catalyzed process and analysis by GC-IRMS gives a smaller than expected value of 1.022 for the carbon kinetic isotope (CKIE), k12/k13. While this value establishes that C-C cleavage is part of the rate-determining process, intrinsic CKIEs for decarboxylation reactions are typically greater than 1.03. Computational analysis of the C-C bond cleavage from 2H+ gives an intrinsic CKIE of 1.051 and suggests two partially rate-determining steps in the decarboxylation of 1: transfer of the second carboxyl proton to the adjacent phenyl carbon and C-C cleavage in which the carboxyl proton is also transferred to water. Applying the principle of microscopic reversibility to fixation of CO2 in acidic solutions reveals the importance of proton transfers to both carbon and oxygen in the overall fixation process.
The molecular and electronic structure of octahedral tris(phenolato)iron(III) complexes and their phenoxyl radical analogues: A Mossbauer and resonance Raman spectroscopic study
Snodin, Michael D.,Ould-Moussa, Lynda,Wallmann, Ursula,Lecomte, Sophie,Bachler, Vinzenz,Bill, Eckhard,Hummel, Helga,Weyhermueller, Thomas,Hildebrandt, Peter,Wieghardt, Karl
, p. 2554 - 2565 (1999)
Hexadentate macrocyclic ligands containing a 1,4,7-triazacyclononane backbone and three N-bound pendent-arm phenolares form extremely stable neutral complexes with Fe(III)Cl3. The octahedral complexes [Fe(III)L] undergo three reversible one-electron oxidation processes to yield the mono- and dications, [FeL]+ and [FeL]2+, which are stable in solution for hours, whereas the trications, [FeL]3+, are only stable in solution on the time scale of a cyclic voltammetric experiment. These oxidations are shown to be ligand- rather than metal-centered. Three coordinated phenoxyl radicals are formed successively as shown conclusively by Mossbauer spectroscopy. The neutral, mono-, di-, and tricationic species each contain an octahedral, high-spin ferric ion (S(Fe) = 5/2), which is intramolecularly, antiferromagnetically coupled to the spin (S = 1/2 ) of the bound phenoxyl ligands to yield an S(t) = 2 ground state for the monocation, and an S(t) = 3/2 ground state for the dications as shown by EPR spectroscopy. The vibrations of the coordinated phenolate are observed by resonance Raman (RR) spectroscopy by excitation in resonance with the phenolate-to-iron charge- transfer (CT) transition above 500 nm or, alternatively, of the coordinated phenoxyl by excitation in resonance with the intraligand π → π* transition at about 410 nm. Use of 18O isotopomers selectively labeled at the phenolic oxygen allowed the identification of the C-O stretching and Fe-O stretching and bending modes. It is shown that the substitution pattern of phenolates and phenoxyls in their respective ortho and para positions and the charge of the complexes have a pronounced influence on the vibrational modes observed.
Polyfuryl(aryl)alkanes and their derivatives. 12. C-fur bond cleavage in the series of polyfuryl(aryl)alkanes
Butin,Stroganova,Kul'nevich
, p. 153 - 157 (1996)
Reactions taking place with cleavage of the C-Fur bond are examined. It was established that disproportionation in two directions, leading to the formation of tris(5-methyl-2-furyl)methane, takes place when 3,4-dimethoxyphenylbis(5-methyl-2-furyl)methane is boiled in an acidic medium. The acid-catalyzed reaction of 5-methylfurfural with ethylene glycol leads to the formation of either 2-(5-methyl-2-furyl)-1,3-dioxolane or tris(5-methyl-2-furyl)methane, depending on the catalyst. The treatment of 2-(5-methyl-2-furyl)-1,3-dioxolane or gemtris(5·methyl-2-furyl)ethane with trityl perchlorate leads to tris(5-methyl-2-furyl)carbenium or bis(5-methyl-2-furyl)methylcarbenium perchlorates respectively. 1996 Plenum Publishing Corporation.
Photo-induced thiolate catalytic activation of inert Caryl-hetero bonds for radical borylation
K?nig, Burkhard,Wang, Hua,Wang, Shun
supporting information, p. 1653 - 1665 (2021/06/17)
Substantial effort is currently being devoted to obtaining photoredox catalysts with high redox power. Yet, it remains challenging to apply the currently established methods to the activation of bonds with high bond dissociation energy and to substrates with high reduction potentials. Herein, we introduce a novel photocatalytic strategy for the activation of inert substituted arenes for aryl borylation by using thiolate as a catalyst. This catalytic system exhibits strong reducing ability and engages non-activated Caryl–F, Caryl–X, Caryl–O, Caryl–N, and Caryl–S bonds in productive radical borylation reactions, thus expanding the available aryl radical precursor scope. Despite its high reducing power, the method has a broad substrate scope and good functional-group tolerance. Spectroscopic investigations and control experiments suggest the formation of a charge-transfer complex as the key step to activate the substrates.
Nickel-Catalyzed Hydrodeoxygenation of Aryl Sulfamates with Alcohols as Mild Reducing Agents
Matsuo, Kasumi,Kuriyama, Masami,Yamamoto, Kosuke,Demizu, Yosuke,Nishida, Koyo,Onomura, Osamu
, p. 4449 - 4460 (2021/08/25)
The nickel-catalyzed hydrodeoxygenation of aryl sulfamates has been developed with alcohols as mild reductants. A variety of functional groups and heterocycles were tolerated in this reaction system to give the desired products in high yields. In addition, the gram-scale process and stepwise cine-substitution were also achieved with high efficiency.
A highly stable all-in-one photocatalyst for aryl etherification: The NiIIembedded covalent organic framework
Chen, Hao,Dong, Wenbo,Hu, Jianxiang,Rao, Li,Wang, Pei,Wang, Shengyao,Xiang, Yonggang,Yang, Yi
, p. 5797 - 5805 (2021/08/23)
The efficient conversion of aryl bromides to the corresponding aryl alkyl ethers by dual nickel/photocatalysis has seen great progress, but difficulties of recycling the photosensitizer or nickel complexes cause problems of sustainability. Here, we report the design of a novel, highly stable vinyl bridge 2D covalent organic framework (COF) containing Ni, which combines the role of photosensitizer and reactive site. The as-prepared sp2c-COFdpy-Ni acts as an efficient heterogeneous photocatalyst for C-O cross coupling. The sp2c-COFdpy-Ni can be completely recovered and used repeatedly without loss of activity, overcoming the limitations of the prior methods. Preliminary studies reveal that strong interlayer electron transfer may facilitate the generation of the proposed intermediate sp2c-COFdpy-NiI in a bimolecular and self-sustained manner. This all-in-one heterogeneous photocatalyst exhibits good compatibility of substrates and tolerance of functional groups. The successful attempt to expand the 2D COFs with this new catalyst into photocatalytic organic transformation opens an avenue for photoredox/transition metal mediated coupling reactions.
Metal-Free Heterogeneous Semiconductor for Visible-Light Photocatalytic Decarboxylation of Carboxylic Acids
Shi, Jiale,Yuan, Tao,Zheng, Meifang,Wang, Xinchen
, p. 3040 - 3047 (2021/03/09)
A suitable protocol for the photocatalytic decarboxylation of carboxylic acids was developed with metal-free ceramic boron carbon nitrides (BCN). With visible light irradiation, BCN oxidize carboxylic acids to give carbon-centered radicals, which were trapped by hydrogen atom donors or employed in the construction of the carbon-carbon bond. In this system, both (hetero)aromatic and aliphatic acids proceed the decarboxylation smoothly, and C-H, C-D, and C-C bonds are formed in moderate to high yields (35 examples, yield up to 93%). Control experiments support a radical process, and isotopic experiments show that methanol is employed as the hydrogen atom donor. Recycle tests and gram-scale reaction elucidate the practicability of the heterogeneous ceramic BCN photoredox system. It provides an alternative to homogeneous catalysts in the valuable carbon radical intermediates formation. Moreover, the metal-free system is also applicable to late-stage functionalization of anti-inflammatory drugs, such as naproxen and ibuprofen, which enrich the chemical toolbox.
Ceramic boron carbonitrides for unlocking organic halides with visible light
Yuan, Tao,Zheng, Meifang,Antonietti, Markus,Wang, Xinchen
, p. 6323 - 6332 (2021/05/19)
Photochemistry provides a sustainable pathway for organic transformations by inducing radical intermediates from substrates through electron transfer process. However, progress is limited by heterogeneous photocatalysts that are required to be efficient, stable, and inexpensive for long-term operation with easy recyclability and product separation. Here, we report that boron carbonitride (BCN) ceramics are such a system and can reduce organic halides, including (het)aryl and alkyl halides, with visible light irradiation. Cross-coupling of halides to afford new C-H, C-C, and C-S bonds can proceed at ambient reaction conditions. Hydrogen, (het)aryl, and sulfonyl groups were introduced into the arenes and heteroarenes at the designed positions by means of mesolytic C-X (carbon-halogen) bond cleavage in the absence of any metal-based catalysts or ligands. BCN can be used not only for half reactions, like reduction reactions with a sacrificial agent, but also redox reactions through oxidative and reductive interfacial electron transfer. The BCN photocatalyst shows tolerance to different substituents and conserved activity after five recycles. The apparent metal-free system opens new opportunities for a wide range of organic catalysts using light energy and sustainable materials, which are metal-free, inexpensive and stable. This journal is
