- Catalytic Transformations of 2-Pyridones by Rhodium-Mediated Carbene Transfer
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An enantioselective cyclopropanation reaction of N-substituted 2-pyridones with diazo compounds has been realized by using a chiral rhodium complex as the catalyst, and the corresponding chiral cyclopropanes could be formed in good yields with high enantioselectivities. Moreover, using acceptor-acceptor dimethyl 2-diazomalonate as the carbene precursor, a novel 1,4-rearrangement of a Boc group from N to C has also been discovered under rhodium catalysis.
- Li, Qiongya,Shao, Ying,Su, Jiahui,Sun, Jiangtao
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supporting information
p. 1637 - 1641
(2022/03/14)
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- Access to N-Substituted 2-Pyridones by Catalytic Intermolecular Dearomatization and 1,4-Acyl Transfer
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A novel rhodium-catalyzed dearomatization of O-substituted pyridines to access N-substituted 2-pyridones has been developed. A computational study suggests a mechanism involving the formation of a pyridinium ylide followed by an unprecedented 1,4-acyl migratory rearrangement from O to C. Furthermore, the chiral dirhodium complexes serve as the catalyst for the asymmetric transformation with excellent enantioselective control. DFT calculations indicate the chirality is transferred from axial chirality to the central stereogenic centre. The stronger π–π interaction and CH–π interaction account for the high enantioselectivity.
- Xu, Guangyang,Chen, Ping,Liu, Pei,Tang, Shengbiao,Zhang, Xinhao,Sun, Jiangtao
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supporting information
p. 1980 - 1984
(2019/01/04)
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- Kinetics and reaction mechanism of aminolyses of benzyl 2-pyridyl carbonate and t-butyl 2-pyridyl carbonate in acetonitrile
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Second-order rate constants (kN) have been measured spectrophotometrically for the reactions of benzyl 2- pyridyl carbonate 3 and t-butyl 2-pyridyl carbonate 4 with a series of alicyclic secondary amines in MeCN at 25.0 ± 0.1 ° C. Substrate 4 is much less reactive than 3 and the steric hindrance exerted by the bulky t-Bu group in 4 has been attributed to its decreased reactivity. The Bronsted-type plots for the reactions of 3 and 4 are linear with ssnuc = 0.57 and 0.45, respectively. Thus, the reactions have been concluded to proceed through a concerted mechanism, although the current reactions were expected to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate T±. It has been proposed that the rate of leaving-group expulsion is accelerated by the intramolecular H-bonding interaction in T± and the "push" provided by the RO group through the resonance interaction. Thus, the enhanced nucleofugality forces the reactions to proceed through a concerted mechanism. The reactivity-selectivity principle (RSP) is not applicable to the current reaction systems, since the reaction of the less reactive 4 results in a smaller ssnuc than that of the more reactive 3. Steric hindrance exerted by the bulky t-Bu group in 4 has been suggested to be responsible for the failure of the RSP. Copyright
- Bae, Ae Ri,Um, Ik-Hwan
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body text
p. 1547 - 1550
(2012/07/28)
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- New Amino-protective Reagents for t-Butoxycarbonylation and Benzyloxycarbonylation of Amines and Amino Acids
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New amino-protective reagents for t-butoxycarbonylation and benzyloxycarbonylation of amines and amino acids have been developed. t-Butyl 2-pyridyl carbonate and t-butyl S-(2-pyridyl) thiocarbonate react cleanly with various amines and amino acids to afford N-Boc amines and N-Boc amino acids in high yields.Benzyl 2-pyridyl carbonate and O-benzyl S-(2-pyridyl) thiocarbonate are also found to be very effective in the benzyloxycarbonylation of amino acids.
- Kim, Sunggak,Lee, Jae In,Yi, Kyu Yang
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p. 3570 - 3575
(2007/10/02)
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- 2(1H)-Pyridone as Leaving Group in Acylation Reactions - Applications in Peptide Synthesis
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Alkyl 2-pyridyl carbonates 3 or mixtures of 3 and the isomeric N-(alkoxycarbonyl)-2-pyridones 3' are useful for the introduction of urethane protective groups into amino acids.The N-protected amino acids 7 - 10 react with 2(1H)-pyridone (1a) using the carbodiimide method to yield 2-pyridyl active esters 11, which easily undergo coupling reactions with amino acid esters 12 with elimination of 1a to give peptides 13 in good yields as well as high optical purities.
- Effenberger, Franz,Brodt, Werner
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p. 468 - 482
(2007/10/02)
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- t-BUTYL 2-PYRIDYL CARBONATE. A USEFUL REAGENT FOR t-BUTOXYLATION OF AMINO ACIDS
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t-Butyl 2-pyridyl carbonate, a stable crystalline compound, is found to be very efficient in the t-butoxycarbonylation of amino acids.
- Kim, Sunggak,Lee, Jae In
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p. 237 - 238
(2007/10/02)
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