- Carbamates: A Directing Group for Selective C-H Amidation and Alkylation under Cp*Co(III) Catalysis
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The selective reactivity of carbamate and thiocarbamate toward alkylation and amidation is reported under stable, high-valent, cost-effective cobalt(III) catalysis. This method reveals the wide possibility of designing a different branch of synthetically
- Bera, Sourav Sekhar,Maji, Modhu Sudan
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supporting information
p. 2615 - 2620
(2020/04/08)
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- Electrochemically Catalyzed Newman-Kwart Rearrangement: Mechanism, Structure-Reactivity Relationship, and Parallels to Photoredox Catalysis
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The facilitation of redox-neutral reactions by electrochemical injection of holes and electrons, also known as "electrochemical catalysis", is a little explored approach that has the potential to expand the scope of electrosynthesis immensely. To systematically improve existing protocols and to pave the way toward new developments, a better understanding of the underlying principles is crucial. In this context, we have studied the Newman-Kwart rearrangement of O-arylthiocarbamates to the corresponding S-aryl derivatives, the key step in the synthesis of thiophenols from the corresponding phenols. This transformation is a particularly useful example because the conventional method requires temperatures up to 300 °C, whereas electrochemical catalysis facilitates the reaction at room temperature. A combined experimental-quantum chemical approach revealed several reaction channels and rendered an explanation for the relationship between the structure and reactivity. Furthermore, it is shown how rapid cyclic voltammetry measurements can serve as a tool to predict the feasibility for specific substrates. The study also revealed distinct parallels to photoredox-catalyzed reactions, in which back-electron transfer and chain propagation are competing pathways.
- Roesel, Arend F.,Ugandi, Mihkel,Huyen, Nguyen Thi Thu,Májek, Michal,Broese, Timo,Roemelt, Michael,Francke, Robert
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p. 8029 - 8044
(2020/07/25)
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- Palladium-catalyzed intramolecular oxidative C-H sulfuration of aryl thiocarbamates
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A palladium-catalyzed intramolecular C-H bond sulfuration reaction of aryl thiocarbamates has been developed. This strategy provides a new route to benzo[d][1,3]oxathiol-2-ones with tolerance of a wide range of substituents. Mechanistic studies suggested
- Zhao, Yingwei,Xie, Yinjun,Xia, Chungu,Huang, Hanmin
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supporting information
p. 2471 - 2476
(2014/09/17)
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- The Newman-Kwart rearrangement: A microwave kinetic study
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(Chemical Equation Presented) The kinetic profile of the Newman-Kwart rearrangement has been evaluated using microwave heating. After first demonstrating equivalence between conventional convective heating and microwave heating, data was gathered and anal
- Gilday, John P.,Lenden, Philip,Moseley, Jonathan D.,Cox, Brian G.
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p. 3130 - 3134
(2008/09/19)
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- The Newman-Kwart rearrangement re-evaluated by microwave synthesis
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The Newman-Kwart rearrangement (NKR) has been re-evaluated by microwave heating. Microwave technology has proven to be ideal for investigating this high temperature rearrangement and facilitated the confirmation of many aspects of this valuable reaction.
- Moseley, Jonathan D.,Sankey, Rosalind F.,Tang, Olivier N.,Gilday, John P.
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p. 4685 - 4689
(2007/10/03)
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- Highly chemoselective methylation and esterification reactions with dimethyl carbonate in the presence of NaY faujasite. The case of mercaptophenols, mercaptobenzoic acids, and carboxylic acids bearing OH substituents
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In the presence of NaY faujasite, the reactions of dimethyl carbonate (DMC) with several ambident nucleophiles such as o- and p-mercaptophenols (1a,b), o- and p-mercaptobenzoic acids (2a,b), o- and p-hydroxybenzoic acids (3a,b), mandelic and phenyllactic acids (4, 5), have been explored under batch conditions. Highly chemoselective reactions can be performed: at 150 °C, compounds 1 and 2 undergo only a S-methylation reaction, without affecting OH and CO2H groups; at 165 °C, acids 3-5 form the corresponding methyl esters, while both their aromatic and aliphatic OH substituents are fully preserved from methylation and/or transesterification processes. Typical selectivities are of 90-98% and isolated yields of products (S-methyl derivatives and methyl esters, respectively) are in the range of 85-96%. A comparative study with K2CO3 as a catalyst is also reported. Although the base (K2CO3) turns out to be more active than the zeolite, the chemoselectivity is elusive: compounds 2a,b undergo simultaneous S-methylation and esterification reactions, and acids 3-5 yield complex mixtures of products of O-methylation, O-methoxycarbonylation, and esterification of their OH and CO2H groups, respectively. Overall, the combined use of a nontoxic reagent/solvent (DMC) and a safe promoter (NaY) imparts a genuine ecofriendly nature to the investigated synthesis.
- Selva, Maurizio,Tundo, Pietro
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p. 1464 - 1470
(2007/10/03)
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- Effects of aromatic thiols on thiol-disulfide interchange reactions that occur during protein folding
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The folding of disulfide containing proteins from denatured protein to native protein involves numerous thiol-disulfide interchange reactions. Many of these reactions include a redox buffer, which is a mixture of a thiol (RSH) and the corresponding disulfide (RSSR). The relationship between the structure of RSH and its efficacy in folding proteins in vitro has been investigated only to a limited extent. Reported herein are the effects of aliphatic and especially aromatic thiols on reactions that occur during protein folding. Aromatic thiols may be particularly efficacious as their thiol pKa values and reactivities match those of the in vivo catalyst, protein disulfide isomerase (PDI). This investigation correlates the thiol pKa values of aromatic thiols with their reactivities toward small molecule disulfides and the protein insulin. The thiol pKa values of nine para-substituted aromatic thiols were measured; a Hammett plot constructed using σp- values yielded ρ = -1.6 ± 0.1. The reactivities of aromatic and aliphatic thiols with 2-pyridyldithioethanol (2-PDE), a small molecule disulfide, were determined. A plot of reactivity versus pKa of the aromatic thiols had a slope (β) of 0.9. The ability of these thiols to reduce (unfold) the protein insulin correlates strongly with their ability to reduce 2-PDE. Since the reduction of protein disulfides occurs during protein folding to remove mismatched disulfides, aromatic thiols with high pKa values are expected to increase the rate not only of protein unfolding but protein folding as well.
- DeCollo,Lees
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p. 4244 - 4249
(2007/10/03)
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- Potassium fluoride on alumina: Synthesis of O-aryl N,N-dimethylthiocarbamates and their rearrangement into S-aryl N,N-dimethylthiocarbamates under microwave irradiation
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A series of O-aryl N,N-dimethyl thiocarbamates have been prepared by the reaction of dimethylthiocarbamoyl chloride with phenols absorbed on potassium fluoride on alumina. The rearrangement of O-aryl N,N-dimethylthiocarbamate into S-aryl N,N-dimethylthiocarbamate under microwave irradiation was also studied. The use of conductive support like graphite or silicon carbide allow these rearrangements although the O-aryl N,N-dimethylthiocarbamates have very low dielectric lost.
- Villemin, Didier,Hachemi, Messaoud,Lalaoui, Mekki
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p. 2461 - 2471
(2007/10/03)
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- Synthesis of a series of focally-substituted organothiol dendrons
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The synthesis of new organothiol-functionalized dendrons of generation 1-4 is described. Several modifications to the original method for preparation of dendrons are detailed that were found to improve the yield and aid in scale-up. A particularly advanta
- Chen, Kang-Yi,Gorman, Christopher B.
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p. 9229 - 9235
(2007/10/03)
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- Triazacyclane-based Trithiols and Their Use in the Preparation of Site-differentiated Iron-Sulfur Clusters
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The new tripodal thiol ligands 1,4,7-tris(4-mercaptobenzoyl)-1,4,7-triazacyclononane (H3L1) and 1,5,9-tris(4-mercaptobenzoyl)-1,5,9-triazacyclododecane (H3L2) have been synthesised and characterised.On reaction with iron-sulfur clust
- Evans, David J.,Garcia, Gabriel,Leigh,G. Jeffery,Newton, Maurice S.,Santana, M. Dolores
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p. 3229 - 3234
(2007/10/02)
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