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on
Varian
CP-Chirasil-DEX
CB
b-cyclodextrin
column
(25 m ꢁ 0.32 mm ꢁ 0.25
lm). Temperature of the detector and
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A. S. Tetrahedron 2007, 63, 3623–3658.
injector was 220 °C, flow = 100 kPa (H2). GC condition: oven 150–
175 °C, rate 1 °C/min. Retention times: 4a: tR = 16.4 min for (S)
and tR = 16.9 min for (R); 4b: tR = 12.4 min for (S) and tR = 12.7 min
for (R).
3. Hall, D. G. Boronic Acids: Preparation, Applications in Organic Synthesis and
Medicine; Wiley-VCH: Weinheim, Germany, 2005.
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4.6. Determination of the absolute configuration of the boron-
containing amides 4a,b
To a 25 mL, two-necked, round-bottomed flask were added ace-
tonitrile (2 mL), enantiopure amide 4a or 4b (ee >99%, 58 mg,
0.2 mmol), CuBr (27 mg, 0.2 mmol) and N-bromosuccinimide
(36 mg, 0.2 mmol). The reaction mixture was stirred at 80 °C for
12 h. After this period, the reaction was then cooled to room tem-
perature and diluted with ethyl ether (5 mL). The ether layer was
washed with 1 M HCl (1 ꢁ 2 mL), 1 M (1 ꢁ NaOH) and brine
(1 ꢁ 2 mL). The organic layer was dried over anhydrous MgSO4
and the solvent then evaporated under reduced pressure. The
crude product was purified by column chromatography using a
mixture of hexane and ethyl acetate (8:2) as eluent.
4.6.1. (R)-N-(1-(4-Bromophenyl)ethyl)acetamide (R)-7a
Yield: 42 mg (87%), white solid (mp: 101.5–103.2 °C). ee >99%,
½
a 2D1
ꢂ
¼ þ72:2 (c 1.02, CHCl3). 1H NMR (200 MHz, CDCl3) d = 1.45
(d, J = 6.9 Hz, 3H), 1.98 (s, 3H), 5.07 (quint, J = 6.9 Hz, 1H), 5.81
(br, 1H), 7.18 (d, J = 8.4 Hz, 2H), 7.45 (d, J = 8.4 Hz, 2H). 13C NMR
(50 MHz, CDCl3) d = 21.77, 23.18, 48.37, 120.98, 127.95, 131.63,
142.50, 169.75.
10. Andrade, L. H.; Barcellos, T. Org. Lett. 2009, 11, 3052–3055.
11. (a) For recent reviews concerning biocatalytic approaches to obtain optically
active amines, see: Ref. 8; (b) Koszelewski, D.; Tauber, K.; Faber, K.; Kroutil, W.
Trends Biotechnol. 2010, 28, 324–332; (c) Turner, N. J. Curr. Opin. Chem. Biol.
2010, 14, 115–121; (d) Gotor-Fernandez, V.; Gotor, V. Curr. Opin. Drug Disc.
2009, 12, 784–797.
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4.6.2. (R)-N-(1-(3-Bromophenyl)ethyl)acetamide (R)-7b
Yield: 44 mg (91%), colourless oil. ee >99%, ½a D21
¼ þ47:6 (c 1.05,
ꢂ
CHCl3). 1H NMR (200 MHz, CDCl3) d = 1.43 (d, J = 7.0 Hz, 3H), 1.96
(s, 3H), 5.04 (quint, J = 7.0 Hz, 1H), 6.41 (br, 1H), 7.20 (m, 2H),
7.37 (dt, J = 6.9 Hz, 2.0 Hz, 1H), 7.43 (s, 1H). 13C NMR (50 MHz,
CDCl3) d = 21.91, 23.14, 48.41, 122.60, 124.94, 129.13, 130.15,
130.19, 146.04, 169.66.
14. Van Rantwijk, F.; Sheldon, R. A. Tetrahedron 2004, 60, 501–519.
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ChemBioChem 2006, 7, 1745–1749.
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Urdiales, E.; Gotor-Fernández, V.; Gotor, V. Adv. Synth. Catal. 2010, 352, 395–
406.
Acknowledgments
The authors thank FAPESP (State of São Paulo Research Founda-
tion) and CNPq (National Counsel of Technological and Scientific
Development) for financial support.
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