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Synlett 2009(8): 1261-1264  
DOI: 10.1055/s-0029-1216731
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

The Synthesis of AraBOX, a New 4,4′-Bis(oxazoline), from Novel Pentitol-Derived Bis-β-amino Alcohols

David Fraina, Fiona Kirbya, Patrick McArdleb, Patrick O’Leary*a
a School of Chemistry, SMACT (Synthetic Methods: Asymmetric Catalytic Transformations), National University of Ireland, Galway, Ireland
Fax: +353(91)525700; e-Mail: patrick.oleary@nuigalway.ie;
b School of Chemistry, National University of Ireland, Galway, Ireland
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Publikationsverlauf

Received 5 February 2009
Publikationsdatum:
17. April 2009 (online)

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Abstract

The preparation of a novel phenyl 4,4′-bis(oxazoline) [AraBOX] is described. The novel ligand is prepared in two efficient steps from a bis-[(O-silyl)β-amino alcohol], via conversion into an intermediate bis(benzamide) followed by a one-pot deprotection-activation-ring closure (DARC) oxazoline formation. To our knowledge, this is the first reported synthesis of an oxazoline ring via this DARC method. The synthesis of two precursor bis-β-amino alcohols, (2R,4R)- and meso-2,4-diaminopentane-1,5-diol, derived from d-(+)-arabitol and xylitol, respectively, is also described.

Key words

asymmetric synthesis - ligand - catalysis - oxazoline - chiral pool

15

(2 R ,4 R )-2,4-Diaminopentane-1,5-diol Dihydrochloride (11)
¹H NMR (400 MHz, D2O): δ = 3.86 (2 H, dd, J = 12.4, 3.7 Hz 2 × one of CH 2OH), 3.71 (2 H, dd, J = 12.4, 6.0 Hz, 2 × one of CH 2OH), 3.56-3.50 (2 H, m, 2 × CHNH2), 2.05 (2 H, t, J = 7.1 Hz, CHCH 2 CH). ¹³C NMR (100 MHz, CDCl3): δ = 60.2 (2 × CH2OH), 49.4 (2 × CHN), 28.8 (CHCH2CH) ppm. IR: 3512, 3333, 3048 (br), 2907, 1490, 1036 cm-¹. Anal. Calcd for C5H16Cl2N2O2: C, 29.00; H, 7.79; N, 13.53. Found C, 29.17; H, 7.63; N, 13.71. [α]D ²² -46.5 (c 0.7, MeOH). The CIF file for this compound has been deposited with the The Cambridge Crystallographic Data Centre (deposition number 719095).

16

meso -2,4-Diaminopentane-1,5-diol Dihydrochloride (12)
¹H NMR (400 MHz, D2O): δ = 3.84 (2 H, dd, J = 12.4, 3.7 Hz 2 × one of CH 2OH), 3.67 (2 H, dd, J = 12.6, 6.0 Hz, 2 × one of CH 2OH), 3.52-3.47 (2 H, m, 2 × CHNH2), 2.08-1.88 (2 H m, CHCH 2CH). ¹³C NMR (100 MHz, CDCl3): δ = 60.5 (2 × CH2OH), 49.2 (2 × CHN), 28.9 (CHCH2CH). IR: 3315 (br), 2927 (br), 1612, 1559, 1513 cm-¹. Anal. Calcd for C5H16Cl2N2O2: C, 29.00; H, 7.79; N, 13.53. Found C, 28.37; H, 7.3; N, 12.53. The CIF file for this compound has been deposited with the The Cambridge Crystallographic Data Centre (deposition number 719096).

18

N , N ′-[(2 R ,4 R )-1,5-Bis{[ tert -butyl(dimethyl)silyl]oxy}-pentane-2,4-diyl]benzamide (13)
¹H NMR (400 MHz, CDCl3): δ = 7.77 (4 H, d, J = 6.9 Hz, 4 × ortho ArH), 7.48-7.35 (6 H, m, 4 × meta ArH, 2 × para ArH), 7.05 (2 H, d, J = 7.8 Hz, 2 × NH), 4.19-4.12 (2 H, m, 2 × CHN), 3.88-3.81 (4 H, m, 2 × CH2O), 2.07 (2 H, t, J = 6 Hz, CHCH 2 CH). ¹³C NMR (100 MHz, CDCl3): δ = 167.5 (2 × HNC=O), 134.5 (2 × ArCC=O), 131.5 (2 × para ArC), 128.6 (4 × ortho ArC), 127.0 (4 × meta ArC), 64.9 (2 × CH2OSi), 49.2 (2 × CHNH2), 33.4 (CHCH2CH), 26.0 (6 × CH3), 18.3 (2 × C), -5.3 [2 × Si(CH3)2]. IR: 3279, 2928, 1629, 1536, 1102, 777, 691 cm-¹. Anal. Calcd for C31H50N2O4Si2: C, 65.25; H, 8.83; N, 4.91. Found: C, 65.25; H, 8.74; N, 4.77. [α]D ²² +52.2 (c 0.9, MeCN).

19

To a solution of 13 (300 mg, 0.525 mmol) and TsF (140mg, 1.155 mmol) in dry MeCN (5 mL) was added DBU (185 µL, 1.115 mmol). The mixture was stirred at reflux overnight, cooled, and concentrated in vacuo. The residue was purified by flash chromatography on SiO2 (PE-EtOAc, 80:20) to yield desired bis(oxazoline) 1 (120 mg, 75%).
4,4′-Methylenebis[(4 R )-2-phenyl-2-oxazoline] (1)
¹H NMR (400 MHz, CDCl3): δ = 7.95 (4 H, d, J = 6.9 Hz, 4 × ortho ArH), 7.49-7.38 (6 H, m, 4 × meta ArH, 2 × para ArH), 4.66 (2 H, app t, J = 8.5 Hz, 2 × one of CH2O), 4.61-4.51 (2 H, m, 2 × CHN), 4.14 (2 H, app t, J = 8 Hz, 2 × one of CH2O), 1.98 (2 H, t, J = 7 Hz, CHCH 2CH). ¹³C NMR (100 MHz, CDCl3): δ = 163.9 (2 × C=N), 131.4 (2 × para ArC), 128.4 (4 × ortho ArC), 128.3 (4 × meta ArC), 127.9 (2 × ArCCN), 73.7 (2 × CHO), 65.5 (2 × CHN), 43.3 (CHCH2CH). IR: 2924, 1720, 1642, 1080, 1025, 779, 688 cm-¹. Anal. Calcd for C19H18N2O2: C, 74.49; H, 5.92; N, 9.14. Found: C, 74.15; H, 5.83; N, 8.75. [α]D ²³ +57.1 (c 0.7, MeCN). The CIF file for this compound has been deposited with the The Cambridge Crystallographic Data Centre (deposition number 719094).