J. Howarth, N. A. Al-Hashimy / Tetrahedron Letters 42 (2001) 5777–5779
5779
Acknowledgements
then cooled to room temperature and water was added.
Subsequently, the mixture was extracted with
dichloromethane (3×30 mL) and the combined extracts
were washed with water (2×20 mL), dried (anhydrous
MgSO4), filtered and the dichloromethane removed in
vacuo to leave 7 as a brown oil (3.20 g, 87% yield). This
was used without purification in the following step. A
small sample of (−)-cis-myrtanyl imidazole 7 was purified
(flash chromatography, silica gel, 10:1 ethylac-
etate:methanol) with the following analytical data:
The authors would like to acknowledge the contribu-
tion to this research by Enterprise Ireland.
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1H NMR (400 MHz, CDCl3) l (ppm)=0.83 (1H, d,
J=9.6 Hz), 1.02 (3H, s), 1.3 (3H, s), 1.45 (1H, m), 1.70
(1H, m), 1.84 (4H, m), 2.27 (1H, m), 2.39 (1H, m), 3.84
(1H, d, J=8.4 Hz) overlapping 3.85 (1H, d, J=8.0 Hz),
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6.81 (1H, s, NCHCH
s, NCHN).
6 ), 6.97 (1H, s, NCHCH6 ), 7.36 (1H,
13C NMR (100 MHz, CDCl3) l (ppm)=19.8 (CH3), 23.8
(CH3), 26.1 (CH2), 28.2 (CH2), 33.2 (CH2), 38.9 (CH2),
41.5 (CH), 43.0 (CH), 43.4 (CH), 52.9 (C), 119.4
(NC6 HCH), 129.6 (NC6 HCH), 137.6 (NCHN).
1,3,5-Tris(bromomethyl)-2,4,6-trimethyl benzene (0.50 g,
1.35 mmol) and (−)-cis-myrtanyl imidazole (1.00 g, 4.80
mmol) in 1,4-dioxane (15 mL) were heated to 100°C for
24 h. The resulting solid, 1,3,5-tris[N-((−)-cis-myrtanyl
imidazolium)methyl]-2,4,6-trimethyl benzene trisbromide,
was collected, rinsed with diethylether (3×100 mL) and
dried to leave a light brown solid in 90% yield. The
trisbromide salt was converted to the trihexafluorophos-
phate salt by dissolving the trisbromide salt in methanol
(ca. 5% w/v) and adding a saturated aqueous solution of
ammonium hexafluorophosphate until no further precipi-
tation occurred. The precipitate was filtered, washed with
methanol and dried, to yield 3 (82%) with the following
analytical data, mp=260–262°C.
1H NMR (400 MHz, CD3COCD3) l (ppm)=0.94 (3H, d,
J=9.6 Hz), 1.10 (9H, s), 1.20 (9H, s), 1.61 (3H, m), 1.93
(21H, m), 2.39 (3H, m), 2.65 (3H, m), 4.31 (6H, d, J=8.8
Hz), 5.77 (9H, s) 7.63 (3H, s, NCH
6 CH), 7.81 (3H, s,
NCHCH), 8.92 (3H, s, NCHN).
6
13C NMR (100 MHz, CH3COCH3) l (ppm)=17.1 (CH3),
19.9 (CH3), 23.8 (CH3), 26.6 (CH2), 28.4 (CH2), 33.8
(CH2), 39.6 (CH2), 42.3 (CH2), 43.1 (CH), 44.5 (CH),
49.6 (CH), 56.3 (C), 123.8 (CH3), 124.5 (CH2), 130.7
(NCH), 136.7 (NCH), 143.1 (NCHN).
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14. A 2×10−2 molar stock solution for each of the four
homochiral imidazolium hexafluorophosphate salts 3–6
in deuterated acetonitrile was prepared. For each salt
four 1H NMR experiments were run. To equal aliquots
of the stock solution, no chiral anion, (R)-2-aminopropi-
onate anion, (S)-2-aminopropionate anion, and both (R)-
and (S)-2-aminopropionate anions were added in an 1:1
ratio (1:1:1 for the racemic mixture), the anions being
dissolved in deuterated water. The experiments were then
run on a Bruker ADVANCE 400 MHz spectrometer.
2-Aminopropionate: 1H NMR (400 MHz, CDCl3) l
(ppm)=1.36 (3H, d, J =7.2 Hz), 3.62 (1H, q, J=7.2 Hz).
11. Dias, H. V. R.; Jin, W. Tetrahedron Lett. 1994, 35, 1365.
12. Arduengo, III, A. J. US Patent 5,077,414, 1991: General
procedure for the synthesis of compounds 3–6 using
1,3,5-tris[N-((−)-cis-myrtanyl imidazolium)methyl]-2,4,6-
trimethyl benzene trishexafluorophosphate 3 as an exam-
ple. Formation of (−)-cis-myrtanyl imidazole: To a
solution of (−)-cis-myrtanylamine (2.86 g, 18.6 mmol)
and aqueous ammonia (1.00 mL, 18.6 mmol) in propan-
1-ol (10 mL), a solution of glyoxal (2.34 mL, 20.00 mmol)
and aqueous formaldehyde (37%, 1.45 mL, 20.0 mmol) in
propan-1-ol (20 mL) were added dropwise. The solution
was then heated to 80°C and left stirring for 2 h. It was