HETEROCYCLES, Vol. 78, No. 11, 2009
2833
Preparation of the (R)- and (S)-MTPA Ester Derivatives of 1a and 2a by a Convenient Mosher
Ester.15 Compounds 1a (0.7 mg) and 2a (0.7 mg) in deuterated pyrindine-d5 (1.0 mL) was transferred into
clean NMR tube. (S)-(+)-α-methoxy-α-trifluromethylphenylacetic acid (MTPA) chlorides (10 µL) was
added into the NMR tube immediately under a N2 gas stream, and then the NMR tube was permitted to
stand at room temperature. After overnight, the reaction was completed to afford the (R)-MTPA ester
derivatives (1b and 2b) of 1a and 2a, respectively. In manner described for 1b and 2b, (S)-MTPA ester
1
derivatives (1c and 2c) of 1a and 2a were obtained. The H-NMR spectra of 1b, 2b, 1c and 2c were
measured with the reaction NMR tubes directly.
1b. (500 MHz, pyridine-d5): δ 5.719 (1H, br s, H-6), 5.040 (1H, dd, J = 11.5, 4.0 Hz, H-1), 2.135 (1H, q,
J = 7.0 Hz, H-11), 2.064 (1H, m, H-9a), 2.045 (1H, m, H-8a), 2.025 (1H, m, H-8b), 1.998 (1H, m, H-2a),
1.830 (1H, m, H-5), 1.690 (1H, m, H-3a), 1.638 (1H, m, H-2b), 1.529 (1H, m, H-3b), 1.485 (1H, m,
H-9b), 1.373 (3H, s, H-14), 1.340 (3H, s, H-15), 1.914 (3H, d, J = 7.0 Hz, H-12), 0.908 (3H, d, J = 7.0 Hz,
H-13).
1c. (500 MHz, pyridine-d5): δ 5.709 (1H, br s, H-6), 5.040 (1H, dd, J = 11.5, 4.0 Hz, H-1), 2.133 (1H, q, J
= 7.0 Hz, H-11), 2.110 (1H, m, H-9a), 2.044 (1H, m, H-8a), 2.012 (1H, m, H-8b), 2.010 (1H, m, H-2a),
1.800 (1H, m, H-5), 1.714 (1H, m, H-3a), 1.642 (1H, m, H-2b), 1.536 (1H, m, H-3b), 1.457 (1H, m,
H-9b), 1.376 (3H, s, H-14), 1.310 (3H, s, H-15), 0.907 (3H, s, J = 7.0 Hz, H-12), 0.888 (3H, d, J = 7.0 Hz,
H-13).
2b. (500 MHz, pyridine-d5): δ 5.289 (1H, br s, H-8), 4.999 (1H, dd, J = 12.5, 3.5 Hz, H-1), 2.496 (1H, m,
9a), 2.496 (1H, m, H-6a), 2.268 (1H, qd, J = 13.5, 3.5, H-2a), 2.144 (1H, q, J = 7.0 Hz, H-11), 2.098 (1H,
m, H-6b), 2.053 (1H, m, H-9b), 1.893 (1H, dt, J = 13.5, 3.5 Hz, H-3a), 1.846 (1H, dq, J = 13.5, 3.5 Hz,
H-2b), 1.567 (1H, td, J = 13.5, 3.5 Hz, H-3b), 1.375 (1H, dd, J = 12.3, 4.5 Hz, H-5), 1.341 (3H, s, H-14),
1.279 (3H, s, H-15), 0.959 (3H, d, J = 7.0 Hz, H-12), 0.956 (3H, d, J = 7.0 Hz, H-13).
2c. (500 MHz, pyridine-d5): δ 5.272 (1H, br s, H-8), 4.999 (1H, dd, J = 12.5, 3.5 Hz, H-1), 2.467 (1H, m,
9a), 2.472 (1H, m, H-6a), 2.277 (1H, qd, J = 13.5, 3.5, H-2a), 2.132 (1H, q, J = 7.0 Hz, H-11), 2.077 (1H,
m, H-6b), 2.040 (1H, m, H-9b), 1.905 (1H, dt, J = 13.5, 3.5 Hz, H-3a), 1.866 (1H, dq, J = 13.5, 3.5 Hz,
H-2b), 1.589 (1H, td, J = 13.5, 3.5 Hz, H-3b), 1.360 (1H, dd, J = 12.3, 4.5 Hz, H-5), 1.352 (3H, s, H-14),
1.247 (3H, s, H-15), 0.939 (3H, d, J = 7.0 Hz, H-12), 0.932 (3H, d, J = 7.0 Hz, H-13).