Beilstein J. Org. Chem. 2013, 9, 155–165.
quantitative range. Furthermore, the catalysts provide very mild 872757 contains the supplementary crystallographic data for
pH conditions, since the pH values are in the range of 9. This is this paper. These data can be obtained free of charge from The
very unusual, since ordinary primary amine catalysts require Cambridge Crystallographic Data Centre via http://
nents [18]. Attempts to employ the metal-free zwitterionic salts
did not succeed for this type of catalyst. The enantiomeric Synthesis of compound 6. The 2-sulfobenzoic anhydride 4,
excesses that could be achieved by the use of 5–8 were R1–4 = Br (0.918 mmol, 459 mg) was dissolved in 7 mL THF.
moderate to good up to 83%, and the origin of chiral induction The mixture was cooled to 0 °C and (1R,2R)-1,2-diaminocyclo-
could be rationalized by means of DFT calculations. It was hexane (0.918 mmol, 105 mg) was added in 5 mL THF. The
found that there is one conformation of the enantio-determining solution was soon thickened by grey precipitate, and the suspen-
transition structure TS-14 that dominates sufficiently because sion was stirred for 24 h. The solvent was removed in vacuum,
steric repulsion of the anisyl groups in the ligand backbone is and the grey solid was purified by crystallization from
minimized.
methanol. Yield: 510 mg, 90%. Mp 348 °C (decomposition); IR
(nujol) ν: 2953, 2854, 1649, 1539, 1456, 1377, 1199, 1086;
1H NMR (300 MHz, DMSO-d6) 1.23–1.47 (4H, m), 1.60–1.80
(2H, m), 1.81–2.05 (2H, m), 2.73–2.81 (1H, m), 3.80–3.84
Experimental
General
Solvents used in chemical conversions were dried by standard (1H, m), 8.02 (3H, s), 8.75 (1H, d, J = 8.8 Hz); 13C NMR
methods and distilled under argon prior to use. The enan- (75.5 MHz, DMSO-d6) 23.71, 24.45, 29.70, 30.64, 50.09,
tiomeric excesses of the chiral 4-hydroxycumarin derivatives 55.85, 124.26, 125.17, 130.47, 132.04, 138.42, 145.56, 166.52;
were determined by chiral HPLC. Unless otherwise specified, HRMS–ESI (m/z): [M + Na]+ calcd for C13H14Br4N2NaO4S,
we employed the La Chrome elite unit from Hitachi together 636.7259; found, 636.7267.
with the chiral column Chiracel AD-H in 25 cm length. The
flow was adjusted to 0.8 mL/min, the pressure was 32 bar and Synthesis of compound 7. The 2-sulfobenzoic anhydride 4,
the detected wavelength λ = 240 nm. The eluent consisted of R1–4 = H (1.102 mmol, 300 mg) was dissolved in 3 mL DCM.
80% hexanes and 20% isopropanol. The enantiomers of the The mixture was cooled to 0 °C, and compound 3 (1.102 mmol,
chiral compounds were identified by reference spectra of race- 300 mg) was added in a mixture of 3 mL DCM and 3 mL
mates and literature data [23].
diethyl ether. The solution was soon clouded by white precipi-
tate, and the suspension was stirred for 24 h. The solvent was
Synthesis of compound 5. The 2-sulfobenzoic anhydride 4, removed in vacuum, and the white solid was purified by column
R1–4 = H (1.751 mmol, 322 mg) was dissolved in 15 mL THF. chromatography on silica gel (ethanol/DCM 1:1). Yield:
The mixture was cooled to 0 °C and (1R,2R)-1,2-diaminocyclo- 377 mg, 75%. Mp 249 °C; IR (nujol) ν: 2970, 2886, 1462,
hexane (1.751 mmol, 200 mg) was added in 5 mL THF. The 1377, 1246, 1177, 820; 1H NMR (300 MHz, CDCl3) 3.56 (3H,
solution was soon thickened by white precipitate, and the s), 3.68 (3H, s), 4.72–4.76 (1H, d, J = 10.7 Hz), 5.76–5.79
suspension was stirred for 24 h. The solvent was removed in (1H, m), 6.29–6.32 (2H, d, J = 7.9Hz), 6.65–6.68 (2H, d, J =
vacuum, and the white solid was purified by crystallization 8.3 Hz), 7.06–7.14 (5H, m), 7.16–7.37 (2H, m), 7.55–7.56
from methanol. Yield: 434 mg, crude, 83% and 307 mg, pure, (1H, m), 8.78–8.80 (1H, d, J = 6.5Hz); 13C NMR (75.5 MHz,
59%. Mp 344 °C (decomposition); IR (nujol) ν: 2970, 1665, CDCl3) 54.93, 55.11, 56.06, 59.84, 113.79, 113.93, 125.55,
1596, 1251, 1141; 1H NMR (300 MHz, D2O) 0.88–1.14 127.41, 128.55, 128.99, 129.49, 129.92, 129.89, 130.16, 133.83,
(4H, m), 1.47–1.56 (2H, m), 1.74–1.98 (2H, m), 2.35–2.54 140.73, 158.94, 159.44, 169.08; HRMS–ESI (m/z): [M + Na]+
(1H, m), 3.38–3.57 (1H, m), 7.29–7.42 (1H, m), 7.40–7.61 calcd for C23H24N2NaO6S, 479.1247; found, 479.1249.
(2H, m), 7.74–7.91 (1H, m); 13C NMR (75.5 MHz, D2O) 24.25,
24.50, 31.21, 33.07, 53.53, 56.57, 127.12, 128.28, 130.13, Synthesis of compound 8. The 2-sulfobenzoic anhydride 4,
131.46, 133.79, 139.07, 174.24; HRMS–ESI (m/z): [M + Na]+ R1–4 = Br (0.918 mmol, 459 mg) was dissolved in a mixture of
calcd for C13H18N2NaO4S, 321.0879; found, 321.0882; X-ray 3 mL DCM and 3 mL THF. The solution was cooled to 0 °C,
crystal data: C13H18N2O4S, M = 298.35 g/mol, space group: and compound 3 (0.918 mmol, 250 mg) was added in a mixture
P212121, a = 8.4485(2) Å, b = 12.1533(4) Å, c = 13.6221(5) Å, of 3 mL DCM and 3 mL THF. The solution was soon clouded
V = 1398.68(8) Å3, Z = 4, ρ = 1.417 g/mL, T = 100(2) K, by grey precipitate, and the suspension was stirred for 24 h. The
λ = 0.71073 Å, µ = 0.246 mm−1, reflections: 3055, observed: solvent was removed in vacuum, and the grey solid was puri-
2842 (I>2σ(I)), parameters refined: 197, R1 = 0.0259, (I>2σ(I)) fied by column chromatography on silica gel (ethanol/DCM
wR2 = 0.0621, GOF = 1.081, all hydrogen atoms fixed in an 1:1). Yield: 267 mg, 38%. Mp 304 °C (decomposition); IR
ideal position, nitrogen-bonded hydrogen refined. CCDC (nujol) ν: 2968, 2845, 2841, 1643, 1614, 1456, 1377, 1246,
163