| 98%; 2% |
With sodium tetrahydroborate; nickel(II) chloride hexahydrate; hydrogen; In methanol; at 0 - 30℃; under 760.051 Torr;Reflux; Inert atmosphere; |
NaBH4 (0:46 g, 12:1 mmol) was added portionwise at 0 C to a stirred solution of NiCl2*6H2O (1:10 g, 4:63 mmol) in methanol (20 mL). Once the addition was complete, the suspension was stirred for 15 min at 0 C followed by refluxing under argon atmosphere for 15 min. Then, the mixture was cooled to room temperature, and unsaturated ketone 3 (1:50 g, 9:25 mmol) was added. The stirred mixture was treated with hydrogen (1 atm) keeping the external temperature at 25 - 30 C. Once the green color of the methanolic solution had disappeared (about 1 - 2 h), the hydrogenation was stopped, and the mixture was filtered. The nickel boride cake was washed with methanol, and the combined filtrates were evaporated under reduced pressure. Then, the residue was treated with saturated aqueous NH4Cl (20 mL) and ethyl acetate (20 mL). The organic phase was separated, and the aqueous phase was extracted with ethyl acetate (10 mL). The combined organic phases were washed with brine (10 mL), dried with Na2SO4, and evaporated under reduced pressure. According to GC analysis, the unpurified reaction mixture contained > 98% of product 1 (tR =21:3 min), 1% of by product 5 (tR =21:6 min) and traces of starting enone 3 (tR =25:5 min). The residue was recrystallized from a mixture of methanol=water (1 : 3) to give pure raspberry ketone1 in a yield of 1:14 g (75%) as colorless crystals;m. p. 82 - 83 C (lit. [12]: m. p. 80 - 82 C). Alternatively, the residue was recrystallized from the mixture of toluene ethyl acetate (4 : 1), the yield of compound 1 being 1:08 g (71%), m. p. 81 - 83 C. - IR (KBr): n =3373 (OH), 1691 (C=O) cm1. - 1H NMR (400 MHz, CDCl3): d =2.14 (s,3H, CH3), 2.71 - 2.76 (m, 2H, CH2), 2.80 - 2.85 (m, 2H,CH2), 6.29 (br s, 1H, OH), 6.75 - 6.79 (m, 2H, aromaticCH), 7.00 - 7.04 (m, 2H, aromatic CH) ppm. The spectral data were similar to those reported in the literature [12, 20]. -MS: m=z (%)=164 (20) [M]+, 149 (5) [M-CH3]+, 131 (3)[M-CH3-H2O]+, 121 (11) [M-CH3CO]+, 107 (100) [M-CH3COCH2]+. - C10H12O2 (164.2): calcd. C 73.15, H 7.37; found C 73.28, H 7.28. |
| 68%; 19% |
With diphenyl diselenide; hypophosphorous acid; In glycerol; at 90℃; for 0.5h;Inert atmosphere; |
General procedure: General procedure for the synthesis of zingerone usingPhSeSePh/glycerol/H3PO2Glycerol (1.0 mL) was added to a 5 mL round-bottomedflask containing 2-methoxy-4-(3-oxo-1-butenyl)phenol 1l(0.5 mmol), diphenyl diselenide 2 (0.5 mmol) and H3PO2(0.2 mL). The reaction mixture was stirred at 90 C undernitrogen atmosphere for 30 min. After that, the reactionmixture was received in water (20 mL), extracted with ethylacetate (3 × 5 mL), dried over MgSO4, and concentratedunder vacuum. The residue was purified by columnchromatography on silica gel using ethyl acetate/hexane(10:90) as the eluent. |
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