2262
S. Satishkumar, M. Periasamy / Tetrahedron: Asymmetry 20 (2009) 2257–2262
30% ethyl acetate in hexane to elute the desired methoxy Tröger’s
127.9, 127.4, 127.2, 126.3, 125.5, 116.5, 114.0, 111.1, 110.5, 78.9,
77.6, 61.9, 58.4, 55.4, 54.7.
base 3, yield: 1.07 g (76%); mp 168–170 °C (lit.15 mp 172–174 °C);
IR (KBr): 3150, 1493, 1431, 1325, 1207, 1095, 960, 896, 829 cmꢀ1
;
1H NMR (CDCl3) d 7.06 (d, 2H, J = 8.8 Hz), 6.74 (d, 2H, J = 8.8 Hz),
6.42 (s, 2H), 4.64 (d, 2H, J = 16.4 Hz), 4.29 (s, 2H), 4.08 (d, 2H,
J = 16.6 Hz), 3.70 (s, 6H); 13C NMR (CDCl3) d 156.0, 140.9, 128.6,
125.9, 113.9, 110.9, 67.2, 58.9, 55.3.
4.4. NMR Shift experiments
NMR shift experiments were performed on a 400 MHz spec-
trometer at 25 °C and the samples for analysis were prepared by
mixing the equimolar amounts of host 3 or 5 with the guests 6–
11. The final volume was adjusted with CDCl3 to 0.5 mL.
4.2. Resolution of methoxy Tröger’s base analogue 3 using
dibenzoyl-L-tartaric acid
Acknowledgements
The dibenzoyl-L-tartaric acid (7.2 g, 20 mmol) and the racemic
methoxy Tröger’s base 3 (5.64 g, 20 mmol) were taken in acetone
(240 mL) and the contents were stirred at 25 °C for 12 h. The pre-
cipitate was collected and crystallized by dissolving in hot acetone.
The crystals were suspended in a mixture of CH2Cl2 (50 mL) and
2 N Na2CO3 and stirred until the dissolution occurred. The organic
layer was separated and the aqueous layer was extracted with
CH2Cl2 (2 ꢂ 25 mL). The combined organic extracts were washed
with brine (10 mL), dried over anhydrous Na2SO4 and evaporated
to obtain the product (R,R)-3 enantiomer (1.7 g, 30% yield, >98%
S.S.K. thanks the CSIR (New Delhi) for research fellowship. DST
support through a J. C. Bose Fellowship grant to M.P. is gratefully
acknowledged. The authors also thank the DST for the 400 MHz
NMR facility under FIST programme and for the National single
crystal X-ray diffractometer facility. We are thankful for the sup-
port of the UGC under the University of Potential for Excellence
(UPE) and the Center for Advanced Study (CAS) and UGC-MHRD
Chemistry Resources Centre programmes.
ee). ½a 2D5
ꢃ
¼ ꢀ242 ꢄ 5 (c 0.22, CHCl3). The filtrate was concentrated
References
and the residue was treated as outlined above to obtain the (S,S)-3
enantiomer (3.7 g, 66% yield, 30% ee). The (S,S)-3 isomer with 30%
ee was further enriched by repeating the resolution experiment
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½
a 2D5
ꢃ
¼ þ236 ꢄ 5 (c 0.22, CHCl3). The samples were also analyzed
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purities.16
4.3. Preparation of the
methoxy Tröger’s base
a,
a0-diphenyl carbinol derivative 5 of
To an oven-dried round-bottomed flask equipped with a stir
bar, septum, cooled under nitrogen, were added chiral methoxy
Tröger’s base 3 (1.12 g, 4 mmol) and 30 mL of dry THF. The solution
was cooled to 0 °C, BF3:OEt2 (0.58 mL, 4.1 mmol) was added and al-
lowed to stir for 15 min. The solution was cooled to ꢀ78 °C and al-
lowed to stir for 10 min. n-BuLi (2.7 mL of 1.6 M solution in
hexanes, 4.1 mmol) was added and the resulting orange–red solu-
tion was stirred for 10 min. Then to this benzophenone (0.75 g,
4.1 mmol, in dry THF) was added slowly through syringe, the or-
ange–red colour disappeared at the end of addition and the solu-
tion was allowed to stir for 45 min at ꢀ78 °C. The reaction was
quenched by the careful addition of cold water (5 mL). The reaction
mixture was extracted in diethyl ether (2 ꢂ 15 mL) and the com-
bined organic extracts were successively washed with water, brine
solution and dried over anhydrous Na2SO4. After removal of the
solvent, the residue was subjected to chromatography on silicagel
using 20% ethyl acetate in hexane to elute the desired amino alco-
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hol 5.16 Yield: 1.07 g (58%); mp 148–150 °C; ½a 2D5
¼ þ27 ꢄ 1 (c 0.5,
ꢃ
CHCl3); IR (KBr): 3416, 3057, 3003, 2924, 2852, 1493, 1344, 1238,
1035, 702 cmꢀ1; 1H NMR (CDCl3) d 7.54 (d, 2H, J = 8 Hz), 7.33–7.13
(m, 9H), 6.91 (d, 1H, J = 8.8 Hz), 6.72 (dd, 1H, J1 = 2.8 Hz, J2 = 6 Hz),
6.65 (dd, 1H, J1 = 2.8 Hz, J2 = 6 Hz), 6.28 (d, 1H, J = 2.8 Hz), 5.75 (s,
1H), 5.58 (d, 1H, J = 2.8 Hz), 4.67 (s, 1H), 4.38 (d, 1H, J = 16.8 Hz),
3.84 (d, 1H, J = 16.8 Hz), 3.61 (s, 3H), 3.54 (d, 1H, J = 13.2 Hz),
3.30 (d, 1H, J = 13.2 Hz), 3.14 (s, 3H); 13C NMR (CDCl3) d 156.4,
155.3, 144.5, 142.1, 141.8, 140.9, 129.7, 128.7, 128.3, 128.2,
16. HPLC analysis of 3 and 5 was carried out on CHIRALCEL OD-H column using
hexane/2-propanol = 95:5 as mobile phase, flow rate: 1.0 mL/min.
17. Crystal data: for complex (ꢀ)2ꢁ(ꢀ)3 molecular formula: C35H32N2O10
MW = 640.63, monoclinic, space group: P21, a = 10.640(2) Å, b = 14.726(3) Å,
c = 11.347(2) Å, b = 114.366(2)°, V = 1619.64 Å3, Z = 2, c = 1.314 mg mꢀ3
= 0.097 mmꢀ1, T = 298(2) K. Of the 14,906 reflections collected, 6356 were
,
q
,
l
unique (Rint = 0.0288).Refinement on all data converged at R1 = 0.0489,
wR2 = 0.1328 (Deposition number CCDC 740895).