다이아조 메탄에 의한 γ-Alkoxy-α,β-unsaturated Acid의 고리첨가반응

Cycloaddition of γ-Alkoxy-α,β-unsaturated Acid with Diazomethane

EXPERIMENTALS

2-Hept-2-ynyloxy-ethanol (6)

To a suspension of 779 mg (32.1 mmol) of NaH in 20 mL of benzene was added 22.3 mL (306 mmol) of ethylene glycohol dropwise at 0 ℃. The solution was refluxed for 2 hrs and cooled to room temperature. To the solution was added 4.0 g (30.6 mmol) of the chloride 5 in 5 mL of benzene. The solution was refluxed for 4 hrs and cooled to room temperature. Water was added and the aqueous layer was separated and extracted with ether three times. The extracts were washed with brine, dried over MgSO4 and concentrated under reduced pressure. The residue was chromatographed on silica gel. Elution with 50% ethylacetate in hexanes gave 3.43 g(72%) of the alcohol 6: IR (film) υ 3417, 2934, 2864, 1638, 1354 cm-1; 1H NMR (300 MHz, CDCl3) δ 4.15 (2H, t, J=2.0 Hz, propargylic Hs), 3.73 (2H, brt, HOCH2-), 3.59 (2H, brt, HOCH2CH2-), 2.20 (1H, tt, J=4.9, 2.0 Hz, propargylic Hs), 2.09 (1H, brt, -OH), 1.52-1.32 (4H, m, CH3(CH2)2-), 0.88 (3H, t, J=7.2 Hz, -CH3) ppm.

4-Hept-2-ynyloxy-2-methyl-but-2-enoic acid methyl ester (9) and 4-Hept-2-ynyloxy-2-methyl-but-2-enoic acid (1)

To a solution of 1.58 mL (18.2 mL) of oxalyl chloride in 20 mL of CH2Cl2 was added 2.58 mL (3.63 mmol) of DMSO at -78 ℃. The solution was stirred for 10 min and then added 1.89 g (12.1 mmol) of the alcohol 6 in 5 mL of CH2Cl2. The resultant white emulsion was stirred for 40 min and 7.43 g (21.3 mmol) of 2-(triphenylphosphanylidene)-propionic acid methyl ester11 was added. The solution was warmed to room temperature and stirred overnight. Water was added and the organic layer was extracted with ether three times. The extracts were washed with brine, dried over MgSO4 and concentrated under reduced pressure. The residue was chromatographed on silica gel. Elution with 10% ethyl acetate in hexanes gave 2.24 g (83%) of the ester 9: IR (film) υ 2956, 2862, 2360, 1720, 1656, 14536, 1253, 1136, 1036 cm−1; 1H NMR (300 MHz, CDCl3) δ 6.80 (1H, t, J=6.1 Hz, vinyl H), 4.21 (2H, d, J=6.1 Hz, allylic Hs), 4.13 (2H, t, J=2.2 Hz, propargylic Hs), 3.73 (3H, s, -OCH3), 2.21 (2H, tt, J= 6.9, 2.2 Hz, propargylic Hs) 1.84 (3H, s, vinyl CH3), 1.50-1.35 (4H, CH3(CH2)2-), 0.89 (3H, t, J=7.1 Hz, -CH3) ppm. The resultant ester was dissolved in the mixture of methanol-water and treated with LiOH-H2O. The solution was stirred overnight and quenched with 3% HCl. The aqueous layer was separated and extracted with CH2Cl2 three times and the extracts were washed with saturated NaHCO3 and then with brine. The residue was concentrated under reduced pressure to afford the acid 1 quantitatively.

The IR shows the broad carboxylic OH at 3443 cm−1; 1H NMR (300 MHz, CDCl3) δ 6.80 (1H, t, J=6.1 Hz, vinyl H), 4.21 (2H, d, J=6.1 Hz, allylic Hs), 4.13 (2H, t, J=2.2 Hz, propargylic Hs), 2.21 (2H, tt, J=6.9, 2.2 Hz, propargylic Hs) 1.84 (3H, s, vinyl CH3), 1.50-1.35 (4H, m, CH3(CH2)2-), 0.89 (3H, t, J=7.1 Hz, -CH3) ppm.

4-(2-Butyl-1-hydroxy-buta-2,3-dienyl)-3-methyl-4,5-dihydro-3H-pyrazole-3-carboxylic acid methyl ester (10)

To a solution of 0.096 mL (0.95 mmol) of diisopropylamine in 1 mL of THF was added 0.380 mL of 2.5 M n-BuLi in hexanes at 0 ℃. The solution was stirred for 10 mins and cooled to -78 ℃ and then added 80 mg (0.38 mmol) of the acid 1 in 1 mL of THF dropwise. The solution was gradually warmed to room temperature over 12 hrs and then quenched with 1 N HCl. The aqueous solution was separated and extracted with ether three times. The extracts were washed with brine, dried over MgSO4 and concentrated under reduced pressure to afford 71 mg of a mixture. The residue was diluted in ether and the solution was treated with an ethereal solution of diazomethane. The excess diazomethane was quenched with acetic acid and the resultant solution was concentrated under reduced pressure. The residue was chromatograped on silica gel. Elution with 10% ethyl acetate in hexanes gave 44 mg (44%) of the pyrazoline 10: IR (film) υ 3422, 2956, 1955, 1738, 1560, 1435, 1247 cm-1; 1H NMR (300 MHz, CDCl3) δ 4.95 and 4.93 (2H, d, J=2.0 Hz, allenic Hs), 4.62 and 4.52 (2H, ABX, JAB=18.0, JAX=8.4, JBX=5.8 Hz, -N2CH2-), 3.99 (1H, brs, -CHOH), 3.71 (3H, s, -OCH3), 2.60 (1H, m, methine H), 2.20 (1H, brs, -OH), 1.92 (2H, m, allylic CH2), 1.66(3H, s, -CH3), 1.50-1.20 (4H, m, -(CH2)2-), 0.87 (3H, t, J=6.0 Hz, -CH3) ppm.

4-Hept-2-ynyloxymethyl-3-methyl-4,5-dihydro-3H-pyrazole-3-carboxylic acid methyl ester (11)

To a solution of 60 mg (0.27 mmol) of the acid 1 in THF was treated with an ethereal solution of diazomethane. The excess diazomethane was quenched with acetic acid and the resultant solution was concentrated under reduced pressure. The residue was chromatograped on silica gel. Elution with 10% ethyl acetate in hexanes gave 46 mg (64%) of the pyrazoline 11: IR spectrum shows the characteristic N=N stratching band at 1556 cm−1; 1H NMR (500 MHz, CDCl3) δ 4.72 and 4.38 (2H, ABX, JAB= 17.8, JAX=8.7, JBX=6.3 Hz, -N2CH2-), 4.06 (2H, s, propargylic CH2), 3.74 (3H, s, -OMe), 3.45 and 3.34 (2H, ABX, JAB=9.2, JAX=6.9 and JBX=6.4, -OCH2), 2.60 (1H, m, methine H), 2.18 (2H, t, J=7.0 Hz, propargylic CH2), 1.52 (3H, s, -CH3), 1.47-1.35 (4H, m, -(CH2)2-), 0.88 (3H, t, J=7.3 Hz, -CH3) ppm: 13C NMR (75 MHz, CDCl3) δ 196.5, 87.6, 76.0, 67.3, 58.9, 58.8, 52.9, 38.2, 30.6, 21.9, 18.3, 15.3, 13.5; Mass (m/z) 267 (M+H), 223, 207, 193, 179, 166, 149, 126, 113 (base peak).