Solvent effects in the enantioselective catalytic-phase-transfer alkylation of polymer-supported glycine-imine tert-butyl ester: Asymmetric solid-phase synthesis of (R)-α-amino acid derivatives

European Journal of Organic Chemistry

Volumn , Issue 15, 2007, Pages 2490-2496

  Kim, Mi Jeong ^a   Jew, Sang Sup ^a   Park, Hyeung Geun ^a   Jeong, Byeong Seon ^b  

^a Seoul National University   (South Korea)

^b Yeungnam University   (South Korea)

Author keywords

amino acids; Phase transfer catalysis; Solid phase synthesis; Solvent effects

Indexed keywords

EID: 34250635168     PISSN: 1434193X     EISSN: 10990690     Source Type: Journal    
DOI: 10.1002/ejoc.200700001     Document Type: Article

References (30)

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23. When only toluene was used without any water along with solid CsOH the chemical yield was 25% and the enantioselectivity was obtained in the ratio of (R)/(S) = 73.0:17.0.
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26. Total amount of solvent (i.e. organic solvent + water) was fixed to 1.05 mL per 100 mg of substrate 3.
27. For this experiment, 1.0, 2.5, 5.0 and 10.0 equiv. of solid CsOH was added, not an aqueous solution, to a premixed solvent mixture (toluene/chloroform/water, 9:1:0.5). After CsOH was completely dissolved, the other reagents were then added.
28. It is quite troublesome to handle solid CsOH because of its highly hygroscopic character.
29. Results from the variation of reaction temperature (e.g. room temp, and -20°C, the other reaction conditions were the same as that of Entry 12 in Table 1 except for the reaction temperature): i) at room temp., reaction time: 72 h, chemical yield: 73%, enantiomeric ratio: (R/S) = 91.0:9.0. ii) at -20°C, reaction time: 144 h, chemical yield: 34%, enantiomeric ratio: (R/ S) = 95.0:5.0.
30. The aldimines have been used in the synthesis of α,α- dialkylamino acids in solution-phase systems. However, the solid-supported aldimines (3 or 8) gave only monoalkylation products under the reaction conditions used in this paper.