Asymmetric reduction of 2-(N -Arylimino)-3,3,3-trifluoropropanoic acid esters leading to chiral 3,3,3-trifluoroalanine and its derivatives

Synlett

Volumn 1995, Issue 7, 1995, Pages 753-754

  Sakai, Takashi ^a   Yan, Fengyang ^a   Uneyama, Kenji ^a  

^a OKAYAMA UNIVERSITY   (Japan)

Author keywords

3,3,3 trifluoroalanine; asymmetric reduction; catecholborane; imino ester; oxazaborolidine

Indexed keywords

EID: 0002980424     PISSN: 09365214     EISSN: 14372096     Source Type: Journal    
DOI: 10.1055/s-1995-5068     Document Type: Article

References (20)

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15. A typical reduction of 2d: To a solution of imino ester 2d (55 mg, 0.20 mmol), (S)-5, 5-diphenyl-2-methyl-3, 4-propano-l, 3, 2-oxazaborolidine (5.5 mg, 0.02 mmol), and 4A molecular sieves in CH2CI2 (1 ml) at room temperature was added catecholborane (2 M in CH2CI2, 0.2 ml, 0.40 mmol) under nitrogen. After being stirred for 24 hours, the reaction was quenched by addition of water and the organic layer was extracted with hexane. Usual workup followed by column chromatographic purification on silica gel gave 3d (51.6 mg, 93 % yield), [a]D-6.45° (c = 0.29, CHCI3).
16. The optical purity (62 % ee) was determined by HPLC analysis using SUMICHIRAL OA-5000 (1 mM aqueous CuSCM).
17. The purity was confirmed by transformation to the MTPA amide.
18. Compound (S, 5)-(-)-5a; [a]D-6.01° (c = 0.94, CHCI3). IR (CH2CI2): 1752, 1738 cm-1. lH NMR (200 MHz, CDCI3): 5 = 3.08 (d, J = 14.2 Hz, 1H, I/2CH2), 3.50 (d, J = 14.2 Hz, 1H, 1/2CH2), 4.82-4.99 (m, 1H, CH), 5.30 (s, 2H, CH2), 6.53 (d, J = 9.14 Hz, 1H, NH). 19F NMR (188 MHz, CDCI3): 5 = 89.66 (d, 7= 7.0 Hz, 3F, CF3).
19. Compound (R, S)-(+)-Sb; mp: 101-101.5 °C. [a]D +6.04° (c = 0.79, CHCI3). IR (CH2CI2): 1752, 1738 cm-1. IH NMR (200 MHz, CDCI3): 8 = 3.02 (d, 7= 14.2 Hz, 1H, 1/2CH.2), 3.43 (d, 7= 14.1 Hz, 1H, 1/2CH2), 4.78-4.95 (m, 1H, CH), 5.30 (s, 2H, CH2), 6.99 (d, 7 = 9.14 Hz, 1H, NH). 19F NMR (188 MHz, CDCI3): 5 = 89.77 (d, 7= 7.3 Hz, 3F, CF3). Anal. Calcd. for C20H24F3NO5S: C, 53.68; H, 5.41; N, 3.13. Found: C, 53.34; H, 5.56; N, 3.36.
20. Details of the analytical data will be fully reported elsewhere.