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3.3.1. (−)-Menthyl (3S,4R)-3-benzoylamino-4-tritylsul-
fanyl-4,5-dihydro-3H-pyrazole-3-carboxylate 4a. [h]2D5=
+125.4 (c 5.03×10−3, CHCl3).
9b/10b, 6:1). The residue was crystallized affording pure
8 or 9. The mother liquors were chromatographed by
flash column chromatography (cyclohexane/AcOEt,
10:1; 1×10 cm, 6 mL/min) giving two fractions: the first
containing acrylate 10, the second compound 8 or 9.
3.3.2. (+)-Menthyl (3R,4S)-3-benzoylamino-4-tritylsul-
fanyl-4,5-dihydro-3H-pyrazole-3-carboxylate 5b. [h]2D5=
−125.4 (c 2.1×10−3, CHCl3).
3.4.1. (−)-Menthyl (1R,2R)-1-benzoylamino-2-tritylsul-
fanyl-cyclopropylcarboxylate 8a. [h]2D5=+152 (c 2.8×
10−3, CHCl3).
1
4a/5b: Oil. IR wmax 3400, 1731, 1670 cm−1; H NMR l
0.64–1.70 (m, 18H), 3.05, 3.97, 4.62 (ABX system,
J=18.9, 9.4, 6.8, 3H), 4.70–4.76 (m, 1H), 7.20–7.99 (m,
20H), 8.35 (s, 1H, exch.); 13C NMR l 14.5–47.3, 42.5,
68.6, 78.3, 88.1, 100.8, 127.3–144.8, 167.0, 168.0; anal.
calcd: C, 74.39; H, 6.71; N, 6.51. Found: C, 74.20; H,
6.63; N, 6.38.
3.4.2. (+)-Menthyl (1S,2S)-1-benzoylamino-2-tritylsul-
fanyl-cyclopropylcarboxylate 9b. [h]2D5=−152 (c 3.0×
10−3, CHCl3).
8a/9b: Mp 179°C (CH2Cl2/iPr2O). IR wmax 3400, 1740,
1
1670 cm−1; H NMR l 0.68–1.81 (m, 18H), 1.24, 2.21,
3.3.3. (−)-Menthyl (3R,4S)-3-benzoylamino-4-tritylsul-
fanyl-4,5-dihydro-3H-pyrazole-3-carboxylate 5a. [h]2D5=
−202 (c 4.8×10−3, CHCl3).
2.66, (ABX system, J 10.2, 7.4, 6.3, 3H), 4.58–4.64 (m,
1H), 5.42 (s, 1H, exch.), 7.24–7.51 (m, 20H); 13C NMR
l 16.3–47.0, 22.6, 29.9, 39.5, 66.9, 75.5, 127.2–144.4,
168.2, 169.5; anal. calcd: C, 77.76; H, 7.01; N, 2.27.
Found: C, 77.40; H, 7.13; N, 2.32.
3.3.4. (+)-Menthyl (3S,4R)-3-benzoylamino-4-tritylsul-
fanyl-4,5-dihydro-3H-pyrazole-3-carboxylate 4b. [h]2D5=
+202 (c 3.0×10−3, CHCl3).
3.4.3. (−)-Menthyl (1S,2S)-1-benzoylamino-2-tritylsul-
fanyl-cyclopropylcarboxylate 9a. [h]2D5=−235 (c 2.8×
10−3, CHCl3).
5a/4b: Mp 112°C (CH2Cl2/iPr2O). IR wmax 3400, 1730,
1
1670 cm−1; H NMR l 0.34–1.67 (m, 18H), 3.10, 4.07,
4.65 (ABX system, J=19.0, 9.4, 6.2, 3H), 4.54–4.65 (m,
1H), 7.20–7.97 (m, 20H), 8.22 (s, 1H, exch.); 13C NMR
l 15.9–46.7, 42.6, 68.2, 79.0, 88.5, 101.2, 127.4–144.7,
167.0, 167.9; anal. calcd: C, 74.39; H, 6.71; N, 6.51.
Found: C, 74.31; H, 6.65; N, 6.40.
3.4.4. (+)-Menthyl (1R,2R)-1-benzoylamino-2-tritylsul-
fanyl-cyclopropylcarboxylate 8b. [h]2D5=+235 (c 3.0×
10−3, CHCl3).
9a/8b: Mp 205°C (CH2Cl2/iPr2O). IR wmax 3400, 1735,
1
1670 cm−1; H NMR l 0.55–1.63 (m, 18H), 1.25, 2.26,
3.3.5. Menthyl (3S*,4R*)-3-benzoylamino-4-tritylsul-
fanyl-3,4-dihydro-2H-pyrazole-3-carboxylate 6a,7b. IR
2.73, (ABX system, J 10.1, 7.5, 6.3, 3H), 4.48–4.61 (m,
1H), 5.09 (s, 1H, exch.), 7.21–7.55 (m, 20H); 13C NMR
l 15.6–46.9, 22.4, 29.7, 39.6, 66.8, 75.6, 127.2–144.2,
168.2, 169.2; anal. calcd: C, 77.76; H, 7.01; N, 2.27.
Found: C, 77.45; H, 6.90; N, 2.24.
1
wmax 3380, 3360, 1730, 1660 cm−1; H NMR l 0.58–1.87
(m, 18H), 4.09, 6.14 (AX system, J 1.4, 2H), 4.59–4.68
(m, 1H), 6.58 (s, 1H, exch.), 7.26–7.67 (m, 20H), 8.05 (s,
1H, exch.).
3.4.5. Menthyl 2-benzoylamino-4-tritylsulfanylbut-2-
1
3.3.6. (−)-Menthyl (3R,4S)-3-benzoylamino-4-tritylsul-
fanyl-4,5-dihydro-3H-pyrazole-3-carboxylate 7a. [h]2D5=
−69 (c 5.1×10−3, CHCl3).
enoate 10a,b. Oil. IR wmax 3400, 1735, 1670 cm−1; H
NMR l 1.03–2.04 (m, 18H), 3.11, 6.27 (AX2 system, J
7.7, 2H), 7.04–7.59 (m, 20H) 7.79 (s, 1H, exch.); 13C
NMR l 16.7–47.5, 31.0, 67.7, 76.3, 126.2, 127.4–144.9,
132.4, 164.3, 165.8; anal. calcd: C, 77.76; H, 7.01; N,
2.27. Found: C, 77.50; H, 7.12; N, 2.11.
3.3.7. (+)-Menthyl (3S,4R)-3-benzoylamino-4-tritylsul-
fanyl-4,5-dihydro-3H-pyrazole-3-carboxylate 6b. [h]2D5=
+69 (c 5.0×10−3, CHCl3).
3.5. General procedure for the synthesis of 1-benzoyl-
amino-2-tritylsulfanyl-cyclopropylcarboxylic acid 12
7a/6b: Mp 172°C (CH2Cl2/iPr2O). IR wmax 3380, 3360,
1
1730, 1660 cm−1; H NMR l 0.58–1.87 (m, 18H), 3.99,
6.29 (AX system, J=1.4, 2H), 4.59–4.68 (m, 1H), 7.12
(s, 1H, exch.), 7.26–7.67 (m, 20H), 7.94 (s, 1H, exch.);
13C NMR l 15.9–47.3, 57.7, 69.8, 77.2, 77.5, 127.6–
133.1, 141.5, 144.5, 167.7, 170.1; anal. calcd: C, 74.39;
H, 6.71; N, 6.51. Found: C, 74.25; H, 6.60; N, 6.38.
Ester 9a (64 mg, 0.104 mmol) or spirooxazolone (Z)-11
(47.6 mg, 0.55 mmol) was suspended in MeOH (1 mL).
A solution of KOH in MeOH (1 mL, 0.31 M) and H2O
(0.1 mL) were added and the mixture was heated at
90°C for 72 h. The solvent was evaporated and the
crude reaction mixture was taken up with H2O (3 mL)
and washed with AcOEt (3 mL). The water was aci-
dified with HCl (1 mL, 10%) and extracted with CH2Cl2
(3×3 mL). After drying with Na2SO4 the solvent was
evaporated and the crude mixture was recrystallized.
Pure acid 12 was obtained when starting from 9a (22
mg, 44%) or 11 (38.7 mg, 78%). Mp 216°C (CH2Cl2/
Et2O); IR wmax 3380, 1720, 1640 cm−1; 1H NMR l
1.03–2.04 (m, 18H), 1.23, 2.24, 2.78 (ABX system, J
3.4. General procedure for the synthesis of cyclopropyl-
amino acids 8/9
The pyrazoline derivative 4 or 5 (98 mg, 0.15 mmol)
1
was melted at 150°C for 10 min. The H NMR and
HPLC analyses revealed the presence of a mixture of
cyclopropane derivative 8 or 9 and the acrylate 10 (4a:
8a/10a, 4.5:1; 5a: 9a/10a, 6.5:1; 4b: 8b/10b, 4.5:1; 5b: