- Radical induced disproportionation of alcohols assisted by iodide under acidic conditions
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The disproportionation of alcohols without an additional reductant and oxidant to simultaneously form alkanes and aldehydes/ketones represents an atom-economical transformation. However, only limited methodologies have been reported, and they suffer from a narrow substrate scope or harsh reaction conditions. Herein, we report that alcohol disproportionation can proceed with high efficiency catalyzed by iodide under acidic conditions. This method exhibits high functional group tolerance including aryl alcohol derivatives with both electron-withdrawing and electron-donating groups, furan ring alcohol derivatives, allyl alcohol derivatives, and dihydric alcohols. Under the optimized reaction conditions, a 49% yield of 5-methyl furfural and a 49% yield of 2,5-diformylfuran were obtained simultaneously from 5-hydroxymethylfurfural. An initial mechanistic study suggested that the hydrogen transfer during this redox disproportionation occurred through the inter-transformation of HI and I2. Radical intermediates were involved during this reaction.
- Huang, Yang,Jiang, Haiwei,Li, Teng,Peng, Yang,Rong, Nianxin,Shi, Hexian,Yang, Weiran
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p. 8108 - 8115
(2021/10/29)
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- Oxo-Rhenium-Catalyzed Radical Addition of Benzylic Alcohols to Olefins
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Although carbon radicals generated from a variety of alcohol derivatives have proven valuable in coupling and addition reactions, the direct use of alcohols as synthetically useful radical sources is less known. In this report, benzylic alcohols are shown to be effective radical precursors for addition reactions to alkenes when treated with triphenylphosphine or piperidine with the catalyst ReIO2(PPh3)2 (I).
- Bandari, Chandrasekhar,Nicholas, Kenneth M.
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supporting information
p. 3320 - 3327
(2020/03/23)
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- Potassium-Zincate-Catalyzed Benzylic C?H Bond Addition of Diarylmethanes to Styrenes
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Direct functionalization of the benzylic C?H bond of diarylmethanes is an important strategy for the synthesis of diarylmethine-containing compounds. However, the methods developed to date for this purpose require a stoichiometric amount (usually more) of either a strong base or an oxidant. Reported here is the first catalytic benzylic C?H bond addition of diarylmethanes to styrenes and conjugated dienes. A potassium zincate complex, generated from potassium benzyl and zinc amide, acts as a catalyst and displays good activity and chemoselectivity. Considering the atom economy of the reaction and the ready availability of the catalyst, this reaction constitutes a practical, efficient method for diarylalkane synthesis.
- Liu, Yu-Feng,Zhai, Dan-Dan,Zhang, Xiang-Yu,Guan, Bing-Tao
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supporting information
p. 8245 - 8249
(2018/02/26)
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- Substituted Hantzsch Esters as Versatile Radical Reservoirs in Photoredox Reactions
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Substituted Hantzsch esters can act as radical reservoirs in photoredox reactions, steadily releasing a carbon radical and a hydrogen atom radical in the absence of an additional electron acceptor. We propose that radical release by substituted Hantzsch esters occurs via a mechanism involving an internal redox cycle. Cinnamidecinnamides, styrenes, α,β-unsaturated acids, and diarylethenes could be alkylated smoothly with these reagents. (Figure presented.).
- Gu, Fangjun,Huang, Wenhao,Liu, Xu,Chen, Wenxin,Cheng, Xu
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supporting information
p. 925 - 931
(2018/01/04)
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- Formal carbon insertion of n-tosylhydrazone into B-B and B-Si bonds: Gem-diborylation and gem-silylborylation of sp3 carbon
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A convenient method is developed to synthesize 1,1-diboronates from the corresponding N-tosylhydrazones. This method is also applicable to synthesize 1-silyl-1-boron compounds. Meanwhile, derivatization and consecutive Pd-catalyzed cross-coupling reaction
- Li, Huan,Shangguan, Xianghang,Zhang, Zhikun,Huang, Shan,Zhang, Yan,Wang, Jianbo
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p. 448 - 451
(2014/04/03)
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- Cyclopropanation of benzylidenemalononitrile with dialkoxycarbenes and free radical rearrangement of the cyclopropanes
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Thermolysis of 2-cinnamyloxy-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (1a) and the analogous 2-benzyloxy-2-methoxy compound (1b) at 110°C, in benzene containing benzylidenemalononitrile, afforded products of apparent regiospecific addition of methoxycarbonyl and cinnamyl (or benzyl) radicals to the double bond. When the thermolysis of 1a was run with added TEMPO, methoxycarbonyl and cinnamyl radicals were captured. Thermolysis of the 2,2-dibenzyloxy analogue (1c) in the presence of benzylidenemalononitrile gave an adduct that is formally the product of addition of benzyloxycarbonyl and benzyl radicals to the double bond. In this case, a radical addition mechanism could be ruled out, because the rate constant for decarboxylation of benzyloxycarbonyl radicals is very large. A mechanism that fits all of the results is predominant cyclopropanation of benzylidenemalononitrile by the dialkoxycarbenes derived from the oxadiazolines, in competition with fragmentation of the carbenes to radical pairs. The cyclopropanes so formed then undergo homolytic ring-opening to the appropriate diradicals. Subsequent β-scission of the diradicals to afford radical pairs, and coupling of those pairs, gives the final products. Thus, both carbene and radical chemistry are involved in the overall processes.
- Merkley,Venneri,Warkentin
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p. 312 - 318
(2007/10/03)
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- Zinc-Promoted Reactions. 1. Mechanism of the Clemmensen Reaction. Reduction of Benzophenone in Glacial Acetic Acid
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The mechanism of the Clemmensen reduction of diaryl ketones was investigated by reducing benzophenone, benzhydryl chloride, and dichlorodiphenylmethane in AcOH under a variety of conditions.Besides diphenylmethane, dimeric products were isolated that were indicative of the formation of radical species.Different product distributions were obtained from reactions run under different conditions.The reduction of deuteriated benzhydryl chloride was also performed.A quite complicated mechanistic pattern, involving ionic and nonionic reactions, emerged from the experimental p icture.Two pathways, connected through the protonated substrate, were recognized.According to the first pathway the reduction is promoted by a SET from Zn to the substrate, leading to the formation of a carbon radical having one zinc atom bound to the oxygen of the carbonyl group.Benzhydryl chloride, benzhydryl acetate, and dichlorodiphenylmethane are involved in the process.The product distributions suggest the occurrence of several SETs, which involve the formation of different radical species.Ionic reactions are responsible for the second route to the reduced products.Nucleophilic displacements also participate to the complex mechanism.
- Vona, Maria Luisa Di,Rosnati, Vittorio
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p. 4269 - 4273
(2007/10/02)
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- Dimeric Metal Complexes as Mediator for Radical C-C Bond-Forming Reactions
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Irradiation of dicarbonyl(η5-cyclopentadienyl)iron dimer 1 or decacarbonyldimanganese (2) in the presence of alkyl halides leads to C-centered radicals which can be trapped by alkenes and yields saturated and/or unsaturated addition products.Carbon radicals are generated via halogen abstraction by the initially formed metal-centered radicals resulting from homolysis of the metal-metal bond of dimeric mediators 1 and 2.No reaction occurs using octacarbonyl dicobalt (3).
- Giese, Bernd,Thoma, Gebhard
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p. 1135 - 1142
(2007/10/02)
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- C-C Bond Formation via Carbon-Centered Radicals Generated from Dicarbonyl(η5-cyclopentadienyl)organoiron Complexes
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Irradiation of benzyldicarbonyl(η5-cyclopentadienyl)iron complex (2) leads to homolytic cleavage of the Fe-C bond.In the presence of activated alkenes, radical addition occurs, and both saturated and unsaturated addition products 7-9 are formed.Photolysis of alkyliron complexes 2, 3, and 20 in the presence of acrylonitrile leads to the same products as the irradiation of the respective acyliron complexes 28-30.This indicates that, under photolytical conditions, alkyl and acyl complexes are in equilibrium with each other.
- Giese, Bernd,Gebhard, Thoma
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p. 1143 - 1155
(2007/10/02)
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