- An efficient and enantioselective Michael addition of aromatic oximes to α,β-unsaturated aldehydes promoted by a chiral diamine catalyst derived from α,α-diphenyl prolinol
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Chiral diamine catalysts 11a–e derived from α,α-diphenyl prolinol were prepared and successfully applied to the Michael addition of aromatic oximes to α,β-unsaturated aldehydes in mediocre to good yields (up to 78%) and good to high enantioselectivities (up to 93% ee).
- Chen, Feng,Ren, Hong-Xia,Yang, Yu,Ji, Shan-Ping,Zhang, Zheng-Bing,Tian, Fang,Peng, Lin,Wang, Li-Xin
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- Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts
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The Br?nsted basicities pKaH (i.e., pKa of the conjugate acids) of 32 pyrrolidines and imidazolidinones, commonly used in organocatalytic reactions, have been determined photometrically in acetonitrile solution using CH acids as indicators. Most investigated pyrrolidines have basicities in the range 16 aH aH aH 12.6) and the 2-imidazoliummethyl-substituted pyrrolidine A21 (pKaH 11.1) are outside the typical range for pyrrolidines with basicities comparable to those of imidazolidinones. Kinetics of the reactions of these 32 organocatalysts with benzhydrylium ions (Ar2CH+) and structurally related quinone methides, common reference electrophiles for quantifying nucleophilic reactivities, have been measured photometrically. Most reactions followed second-order kinetics, first order in amine and first order in electrophile. More complex kinetics were observed for the reactions of imidazolidinones and several pyrrolidines carrying bulky 2-substituents, due to reversibility of the initial attack of the amines at the electrophiles followed by rate-determining deprotonation of the intermediate ammonium ions. In the presence of 2,4,6-collidine or 2,6-di-tert-butyl-4-methyl-pyridine, the deprotonation of the initial adducts became faster, which allowed the rate of the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k2 followed the correlation log?k2(20 °C) = sN(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and sN. In this way, the organocatalysts A1-A32 were integrated in our comprehensive nucleophilicity scale, which compares n-, -, and σ-nucleophiles. The nucleophilic reactivities of the title compounds correlate only poorly with their Br?nsted basicities.
- An, Feng,Maji, Biplab,Min, Elizabeth,Ofial, Armin R.,Mayr, Herbert
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supporting information
p. 1526 - 1547
(2020/02/04)
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- In search of diamine analogs of the α,α-diphenyl prolinol privileged chiral organocatalyst. Synthesis of diamine derivatives of α,α-diphenyl-(S)-prolinol and their application as organocatalysts in the asymmetric Michael and Mannich reactions
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This paper describes improved reaction conditions for the substitution of the hydroxyl group in (S)-diphenyl(pyrrolidin-2-yl)methanol by the azide group, which was then reduced to the diamine derivative. We examined two protecting groups (N-Bn and N-Boc) on the pyrrolidine nitrogen in order to functionalize the primary amino group into various amide, alkylated amine, sulfonamide, thiourea and triazole derivatives. Notably, carefully controlled conditions were required to generate the desired derivatives from the sterically hindered benzhydrylamine moiety. Unexpectedly, upon removal of the N-protecting group in derivatives containing electrophilic polar double bonds (C=S, C=O) cyclization took place, affording products such as amidines. The target compounds were evaluated as bifunctional organocatalysts in the asymmetric Michael and Mannich addition reactions. (S)-2-(Azidodiphenylmethyl)pyrrolidine (S)-7 was identified as the most efficient organocatalyst among the various diamine derivatives of α,α-diphenyl-(S)-prolinol prepared in this work.
- Reyes-Rangel, Gloria,Vargas-Caporali, Jorge,Juaristi, Eusebio
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supporting information
p. 379 - 391
(2015/12/31)
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- Protective group-free synthesis of new chiral diamines via direct azidation of 1,1-diaryl-2-aminoethanols
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A direct azidation of tertiary alcohols using sodium azide-sulfuric acid is described; the present method provides an efficient and practical path for the synthesis of new chiral diamines from unmasked 1,1-diaryl-2-aminoethanols derived from natural amino
- Roy, Harendra Nath,Pitchaiah, Arigala,Kim, Miri,Hwang, In Taek,Lee, Kee-In
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p. 3526 - 3530
(2013/04/10)
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- (S)-proline-derived catalysts for the acylative kinetic resolution of alcohols: A remote structural change allows a complete selectivity switch
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A systematic preliminary study has identified a suite of catalysts, all readily prepared and derived from (S)-proline, which differ by a remote substituent only. If this substituent is capable of hydrogen-bond donation the catalyst will promote the resolu
- Gleeson, Oliver,Gun'Ko, Yurii K.,Connon, Stephen J.
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supporting information
p. 1728 - 1734
(2013/09/02)
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- Catalytic asymmetric formal [4 + 1] annulation leading to optically active cis -isoxazoline N -oxides
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The catalytic asymmetric synthesis of densely functionalized cis-isoxazoline N-oxides was realized with novel use of an organocatalyst, (S)-2-(azidodiphenylmethyl)pyrrolidine (4e) (Tan, B.; Zhu, D.; Zhang, L.; Chua, P. J.; Zeng, X.; Zhong, G. Chem.-Eur. J
- Shi, Zugui,Tan, Bin,Leong, Wendy Wen Yi,Zeng, Xiaofei,Lu, Min,Zhong, Guofu
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supporting information; experimental part
p. 5402 - 5405
(2011/02/26)
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