- Asymmetric trifluoromethylthiolation of azlactones under chiral phase transfer catalysis
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The first enantioselective method for the installation of the SCF3 group at the C-4 position of azlactones is described in the present communication under quinidinium phase transfer catalysis. The higher performance of substrates containing electron-rich 2-aryl groups at the azlactone was rationalized using DFT calculations.
- Alemán, José,Bernardi, Luca,Borello, Fabio,Cano, Rafael,Capaccio, Vito,Díaz-Tendero, Sergio,De Riccardis, Francesco,Della Sala, Giorgio,Rodríguez, Ricardo I.,Sicignano, Marina
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supporting information
p. 2914 - 2920
(2020/04/28)
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- Catalytic Aerobic Cross-Dehydrogenative Coupling of Azlactones en Route to α,α-Disubstituted α-Amino Acids
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We developed a catalytic aerobic method to synthesize α,α-disubstituted α-amino acids through cross-dehydrogenative coupling of azlactones. Combining an iron catalyst with a bisoxazolidine ligand resulted in high catalytic performance, and cross-coupling with an indole proceeded smoothly under aerobic conditions. A wide variety of α-aryl and aliphatic amino acid derived azlactones were applied to the present catalysis. In addition, a quaternary carbon could be constructed using oxindole and benzofuranone under aerobic conditions.
- Tsuji, Taro,Tanaka, Takafumi,Tanaka, Tsukushi,Yazaki, Ryo,Ohshima, Takashi
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supporting information
p. 4164 - 4170
(2020/06/04)
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- Rational Design of 2-Substituted DMAP- N-oxides as Acyl Transfer Catalysts: Dynamic Kinetic Resolution of Azlactones
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A novel concept that conversion of chiral 2-substituted DMAP into its DMAP-N-oxide could significantly enhance the catalytic activity and still be used as an acyl transfer catalyst is presented. A new type of chiral 2-substituted DMAP-N-oxides, derived from l-prolinamides, has been rationally designed, facilely synthesized, and applied in the dynamic kinetic resolution of azlactones. Using simple MeOH as the nucleophile, various l-amino acid derivatives were produced in high yields (up to 98% yield) and enantioselectivities (up to 96% ee). Furthermore, α-deuterium labeled l-phenylalanine derivative was also obtained. Experiments and DFT calculations revealed that in 2-substituted DMAP-N-oxide, the oxygen atom acted as the nucleophilic site and the N-H bond functioned as the H-bond donor. High enantioselectivity of the reaction was governed by steric factors, and the addition of benzoic acid reduced the activation energy by participating in the construction of a H-bond bridge. The theoretical chemical study indicated that only when attack directions of the chiral catalyst were fully considered could the correct calculation results be obtained. This work paves the way for the utilization of the C2 position of the pyridine ring and the development of chiral 2-substituted DMAP-N-oxides as efficient acyl transfer catalysts.
- Deng, Yun,Guo, Hai-Ming,Huang, Bin,Li, Ning,Qu, Gui-Rong,Tian, Yin,Wu, Xiao-Xia,Xie, Ming-Sheng
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supporting information
p. 19226 - 19238
(2020/11/13)
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- Strategy for Catalytic Chemoselective Cross-Enolate Coupling Reaction via a Transient Homocoupling Dimer
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A new strategy, a transient homocoupling dimer strategy, for direct catalytic oxidative cross-enolate coupling reactions is developed. Cross-enolate coupling products bearing a (contiguous) tetrasubstituted carbon center were obtained chemoselectively without the need for stoichiometric amounts of strong bases/metal oxidants, and thus, the present catalysis provides a general method for the synthesis of unnatural α,α-disubstituted amino acid motifs. The distinct transformation of azlactone and 2-acylimidazole units highlighted the synthetic utility of the present catalysis.
- Tanaka, Takafumi,Tanaka, Tsukushi,Tsuji, Taro,Yazaki, Ryo,Ohshima, Takashi
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supporting information
p. 3541 - 3544
(2018/06/26)
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- Regiodivergent Enantioselective γ-Additions of Oxazolones to 2,3-Butadienoates Catalyzed by Phosphines: Synthesis of α,α-Disubstituted α-Amino Acids and N,O-Acetal Derivatives
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Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective γ-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective γ-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronucleophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective γ-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched α,α-disubstituted α-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and γ-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nucleophilic oxazolide and the electrophilic phosphonium intermediate.
- Wang, Tianli,Yu, Zhaoyuan,Hoon, Ding Long,Phee, Claire Yan,Lan, Yu,Lu, Yixin
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supporting information
p. 265 - 271
(2016/01/25)
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- Probing the efficiency of N-heterocyclic carbene promoted O- to C-carboxyl transfer of oxazolyl carbonates
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(Chemical Equation Presented) Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
- Thomson, Jennifer E.,Campbell, Craig D.,Concellon, Carmen,Duguet, Nicolas,Rix, Kathryn,Slawin, Alexandra M. Z.,Smith, Andrew D.
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p. 2784 - 2791
(2008/09/20)
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