反应详情

温度

20 °C

2,3-Dimethyl-1,3-butadiene (10.16 g, 123.72 mmol), ethyl acrylate (11.06 g, 110.47 mmol) and hydroquinone (0.12 g, 1.11 mmol) were heated with stirring at 165° C. in a sealed tube for 16 h and then at 205° C. for an additional 4 h. Kugelrohr distillation of the resulting residue at 150° C. and 0.5 torr gave 14.11 g (70%) of cyclohexene ester 1 as an oil in the 20° C. bulb. To a solution of the ester 1 (13.62 g, 72.32 mmol) in anhydrous THF (200 ml) at −78° C. under argon added the LiAlH4 (54.30 ml, 1 M in diethyl ether). This mixture was stirred for 1 h at 20° C. and then quenched at 0° C. by the careful, consecutive addition of H2O (2.06 ml), NaOH (2.06 ml of a 15% aqueous solution), and an additional portion of H2O (6.18 ml). The solids were filtered off and the filtrate was concentrated under reduced pressure. Kugelrohr distillation of the resulting residue at 150-180° C. and 0.5 torr gave 9.98 g (98%) of the alcohol 2 as a colorless volatile oil in the 0° C. bulb. To a solution of triphenyl phosphine (27.13 g, 103.45 mmol), and imidazole (7.04 g, 103.45 mmol) in anhydrous benzene (450 ml) under argon was added the I2 (22.75 g, 89.61 mmol) in benzene (170 ml) over a period of 10 minutes with rapid mechanical stirring. After an additional 10 minutes the alcohol 2 (9.23 g, 65.89 mmol) in benzene (100 ml) was added to this rapidly stirring mixture over a period of 5 minutes. After 2 h the reaction was diluted with hexanes (800 ml) and the solids were filtered off. The organics were washed with 3 portions of H2O (800 ml), dried (MgSO4), filtered and concentrated under reduced pressure. The residual solids were filtered off and the resulting oil was purified by kugelrohr distillation at 200° C. and 0.5 torr to give 11.99 g (73%) of the iodide 3 as a pale oil in the 0° C. bulb. To a solution of the previously described 1-N-(dimethylsulfamoyl)-2-tert-butyldimethylsilyl imidazole (4.34 g, 15.00 mmol) in anhydrous THF (50 ml) at −78° C. under argon was added n-butyllithium (5.76 ml, 2.5 M in hexanes). This mixture was stirred for 10 minutes at −10° C. and then cooled to −20° C. before adding the iodide 3 (3.00 g, 12.00 mmol) in THF (25 ml) dropwise via cannula. The resulting solution was stirred for 16 h at 20° C., then quenched with saturated aqueous NaHCO3 and concentrated under reduced pressure. The residues were taken up in diethyl ether and washed consecutively with H2 and brine, dried (MgSO4) and concentrated. Subsequent purification by chromatography on SiO2 with 5-10% EtOAc:hexanes gave 0.89 g (15%) of the imidazole 4 as a pale oil. To a solution of imidazole 4 (0.89 g, 2.17 mmol) in anhydrous THF (25 ml) under argon was added tetrabutylammonium fluoride (2.38 ml, 1 M in THF) and the resultant solution was stirred for 1 h at 20° C. The mixture was concentrated under reduced pressure and the residues were taken up in diethyl ether and washed consecutively with saturated aqueous NaHCO3 and brine, dried (MgSO4) and concentrated. The residues were purified by chromatography on SiO2 with 50% EtOAc:hexanes to give 0.56 g (87%) of the imidazole 5 as a pale oil. To a solution of 5 (0.53 g, 1.77 mmol) in MeOH (5 ml) was added aqueous KOH (15 ml of a 5M solution) and the mixture was heated at reflux for 32 h. The mixture was concentrated under reduced pressure, diluted with H2O (5 ml) and extracted exhaustively with CHCl3. The combined organic fractions were washed consecutively with H2O and brine, dried (MgSO4) and concentrated under reduced pressure. The imidazole was recrystallized by stirring in MeOH with an equimolar amount of fumaric acid until all solids had disappeared followed by the addition of a small amount of diethyl ether. The title compound 6 (W-1) 0.27 g (57%) was recovered as pale crystals.

1. customquenched at 0° C. by the careful,
2. additionconsecutive addition of H2O (2.06 ml), NaOH (2.06 ml of a 15% aqueous solution), and an additional portion of H2O (6.18 ml)
3. filtrationThe solids were filtered off
4. concentrationthe filtrate was concentrated under reduced pressure
5. distillationKugelrohr distillation of the resulting residue at 150-180° C.