28819-26-3Relevant articles and documents
Reduction of Electron-Deficient Alkenes Enabled by a Photoinduced Hydrogen Atom Transfer
Larionova, Natalia A.,Ondozabal, Jun Miyatake,Cambeiro, Xacobe C.
, p. 558 - 564 (2020/12/07)
Direct hydrogen atom transfer from a photoredox-generated Hantzsch ester radical cation to electron-deficient alkenes has enabled the development of an efficient formal hydrogenation under mild, operationally simple conditions. The HAT-driven mechanism is supported by experimental and computational studies. The reaction is applied to a variety of cinnamate derivatives and related structures, irrespective of the presence of electron-donating or electron-withdrawing substituents in the aromatic ring and with good functional group compatibility. (Figure presented.).
Radical Chain Reduction via Carbon Dioxide Radical Anion (CO2?-)
Hendy, Cecilia M.,Smith, Gavin C.,Xu, Zihao,Lian, Tianquan,Jui, Nathan T.
, p. 8987 - 8992 (2021/07/01)
We developed an effective method for reductive radical formation that utilizes the radical anion of carbon dioxide (CO2?-) as a powerful single electron reductant. Through a polarity matched hydrogen atom transfer (HAT) between an electrophilic radical and a formate salt, CO2?- formation occurs as a key element in a new radical chain reaction. Here, radical chain initiation can be performed through photochemical or thermal means, and we illustrate the ability of this approach to accomplish reductive activation of a range of substrate classes. Specifically, we employed this strategy in the intermolecular hydroarylation of unactivated alkenes with (hetero)aryl chlorides/bromides, radical deamination of arylammonium salts, aliphatic ketyl radical formation, and sulfonamide cleavage. We show that the reactivity of CO2?- with electron-poor olefins results in either single electron reduction or alkene hydrocarboxylation, where substrate reduction potentials can be utilized to predict reaction outcome.
Stereodivergent Synthesis of Alkenylpyridines via Pd/Cu Catalyzed C-H Alkenylation of Pyridinium Salts with Alkynes
Chen, Hua,Haiyan, Fu,Jiang, Weidong,Li, Ruixiang,Li, Shun,Li, Wenjing,Tang, Juan,Xu, Bin,Yuan, Maolin,Zheng, Xueli
, p. 7814 - 7819 (2020/11/03)
The first Pd/Cu catalyzed selective C2-alkenylation of pyridines with internal alkynes has been developed via the pyridinium salt activation strategy. Importantly, the configuration of the product alkenylpyridines could be tuned by the choice of the proper N-alkyl group of the pyridinium salts, thus allowing for both the Z- and E-alkenylpyridines synthesized with good regio- and stereoselectivity. A plausible mechanism was proposed based on the Hammett study and KIE experiment.
One and Two-Carbon Homologation of Primary and Secondary Alcohols to Corresponding Carboxylic Esters Using β-Carbonyl BT Sulfones as a Common Intermediate
Bon, David J.-Y. D.,Ková?, Ond?ej,Ferugová, Vendula,Zále?ák, Franti?ek,Pospí?il, Ji?í
, p. 4990 - 5001 (2018/05/17)
Herein we report the efficient one- and two-carbon homologation of 1° and 2° alcohols to their corresponding homologated esters via the Mitsunobu reaction using β-carbonyl benzothiazole (BT) sulfone intermediates. The one-carbon homologation approach uses standard Mitsunobu C-S bond formation, oxidation and subsequent alkylation, while the two-carbon homologation uses a less common C-C bond forming Mitsunobu reaction. In this latter case, the use of β-BT sulfone bearing esters lowers the pKa sufficiently enough for the substrate to be used as a carbon-based nucleophile and deliver the homologated β-BT sulfone ester, and this superfluous sulfone group can then be cleaved. In this paper we describe several methods for the effective desulfonylation of BT sulfones and have developed methodology for one-pot alkylation-desulfonylation sequences. As such, overall, a one-carbon homologation sequence can be achieved in a two-pot (four step) procedure and the two-carbon homologation in a two-pot (three step) procedure (three-pot; four step when C-acid synthesis is included). This methodology has been applied to a wide variety of functionality (esters, silyl ethers, benzyls, heteroaryls, ketones, olefins and alkynes) and are all tolerated well providing good to very good overall yields. The power of our method was demonstrated in site-selective ingenol C20 allylic alcohol two-carbon homologation.
Conversion of alcohols to alkyl esters and carboxylic acids using heterogeneous palladium-based catalysts
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Sheet 3; 12, (2017/04/28)
Disclosed are methods for synthesizing an ester or a carboxylic acid from an organic alcohol. To form the ester one reacts, in the presence of oxygen gas, the alcohol with methanol or ethanol. This reaction occurs in the presence of a catalyst comprising palladium and a co-catalyst comprising bismuth, tellurium, lead, cerium, titanium, zinc and/or niobium (most preferably at least bismuth and tellurium). Alternatively that catalyst can be used to generate an acid from that alcohol, when water is also added to the reaction mix.
Discovery of multicomponent heterogeneous catalysts via admixture screening: PdBiTe catalysts for aerobic oxidative esterification of primary alcohols
Mannel, David S.,Ahmed, Maaz S.,Root, Thatcher W.,Stahl, Shannon S.
supporting information, p. 1690 - 1698 (2017/02/10)
In the present study, we demonstrate the utility of "admixture screening" for the discovery of new multicomponent heterogeneous Pd catalyst compositions that are highly effective for aerobic oxidative methyl esterification of primary alcohols. The identification of possible catalysts for this reaction was initiated by the screening of simple binary and ternary admixtures of Pd/charcoal in combination with one or two metal and/or metalloid components as the catalyst. This approach permitted rapid evaluation of over 400 admixture combinations for the oxidative methyl esterification of 1-octanol at 60°C in methanol. Product yields from these reactions varied widely, ranging from 2% to 88%. The highest yields were observed with Bi-, Te-, and Pb-based additives, and particularly from those containing both Bi and Te. Validation of the results was achieved by preparing specific PdBiTe catalyst formulations via a wet-impregnation method, followed by application of response surface methodology to identify the optimal Pd-Bi-Te catalyst stoichiometry. This approach revealed two very effective catalyst compositions: PdBi0.47Te0.09/C (PBT-1) and PdBi0.35Te0.23/C (PBT-2). The former catalyst was used in batch aerobic oxidation reactions with different primary alcohols and shown to be compatible with substrates bearing heterocycle and halide substituents. The methyl ester products were obtained in >90% yield in nearly all cases. Implementation of the PBT-2 catalyst in a continuous-flow packed-bed reactor achieved nearly 60 000 turnovers with no apparent loss of catalytic activity.
Copper-Catalyzed Silylcupration of Activated Alkynes
Vercruysse, Sébastien,Jouvin, Kévin,Riant, Olivier,Evano, Gwilherm
, p. 3373 - 3381 (2016/09/12)
A highly efficient catalytic silylcupration of activated alkynes is reported. Upon reaction with silylboronates and methanol in THF at room temperature in the presence of copper(I) fluoride tris(triphenylphosphine), a range of ynamides and propiolates were found to undergo a smooth silylcupration. This reaction, which tolerates various functional groups, affords a straightforward and efficient entry to the corresponding β-silylenamides and -acrylates, which were formed with high levels of regio- and stereoselectivities.
Aerobic oxidation of diverse primary alcohols to methyl esters with a readily accessible heterogeneous Pd/Bi/Te catalyst
Powell, Adam B.,Stahl, Shannon S.
supporting information, p. 5072 - 5075 (2013/10/22)
Efficient aerobic oxidative methyl esterification of primary alcohols has been achieved with a heterogeneous catalyst consisting of 1 mol % Pd/charcoal (5 wt %) in combination with bismuth(III) nitrate and tellurium metal. The Bi and Te additives significantly increase the reaction rate, selectivity, and overall product yields. This readily accessible catalyst system exhibits a broad substrate scope and is effective with both activated (benzylic) and unactivated (aliphatic) alcohols bearing diverse functional groups.
Visible light-induced selective generation of radicals from organoborates by photoredox catalysis
Yasu, Yusuke,Koike, Takashi,Akita, Munetaka
supporting information, p. 3414 - 3420 (2013/02/25)
A new strategy for the generation of carbon-centered radicals via oxidation of alkyl-, allyl-, benzyl- and arylborates by visible-light-driven single electron transfer (SET) photoredox catalysis has been established. The generated radicals smoothly react with TEMPO and electron-deficient alkenes to afford C-O and C-C coupling products, respectively. In this radical initiating system, cyclic organo(triol)borates turn out to be useful radical precursors.
N-Heterocyclic carbene-catalyzed oxidations
Maki, Brooks E.,Chan, Audrey,Phillips, Eric M.,Scheidt, Karl A.
experimental part, p. 3102 - 3109 (2009/09/05)
N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazolium intermediate generated under catalytic conditions can be employed as a chiral acylating agent in the desymmetrization of meso-diols.
