反应详情

According to the process described in the literature (JP83-118577), methyl 1,4-dioxaspiro[4.5]decan-8-carboxylate was reacted with methyl iodide in the presence of LDA (lithium diisopropylamide) to obtain methyl 8-methyl-1,4-dioxaspiro[4.5]decan-8-carboxylate (the compound (1) of the above figure). (The starting material was synthesized according to the processes described in the literature by Rosemmund et al. (Chem. Ber., 1975, Vol. 108, pp. 1871-1895) and the literature by Black et al. (Synthesis, 1981, p. 829).) (2) A mixture comprising 3.80 g of the compound obtained in the above (1), 3.55 g of sodium hydroxide, 16 mL of methanol and 25 mL of water was refluxed for 2 hours. The reaction mixture was ice-cooled, adjusted to pH 5 by 2N hydrochloric acid and an aqueous 10% citric acid solution, and extracted with ethyl acetate. The extract was washed with water and brine, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure to obtain 3.46 g of 8-methyl-1,4-dioxaspiro[4.5]decan-8-carboxylic acid (the compound (2) of the above figure). (3) A mixture comprising 16.19 g of the compound obtained in the above (2), 24.51 g of diphenylphosphoryl azide, 9.00 g of triethylamine and 160 mL of toluene was refluxed for 2.5 hours. The-reaction mixture was ice-cooled, washed with an aqueous saturated sodium hydrogencarbonate solution, water and brine, and dried over anhydrous sodium sulfate. Subsequently, the solvent was removed under reduced pressure. 9.55 g of potassium tert-butoxide was slowly added to 100 mL of a dimethylacetamide solution containing the resulting compound under ice-cooling; and the mixture was stirred at room temperature for 1 hour. The reaction mixture was poured into ice-water, and the precipitated crystal was collected by filtration, washed with water and dried. To 100 mL of a tetrahydrofuran solution containing the resulting compound was added 100 mL of an aqueous solution containing 30.87 g of p-toluenesulfonic acid hydrate, and the mixture was stirred at room temperature for 16 hours. The mixture was diluted with an aqueous saturated sodium hydrogencarbonate solution and extracted with ethyl acetate. The extract was washed with water and brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to obtain 10.41 g of 4-tert-butoxycarbonylamino-4-methylcyclohexanone (the compound (3) of the above figure). (4) A mixture comprising 10.41 g of the compound obtained in the above (3), 11.01 g of sodium triacetoxyborohydride, 5.10 mL of benzylamine and 150 mL of methylene chloride was stirred at room temperature for 16 hours. The mixture was diluted with an aqueous saturated sodium hydrogencarbonate solution and extracted with ethyl acetate. The extract was washed with water and brine, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure. To 15 mL of a methanol solution containing the resulting compound were added 3.32 g of p-toluenesulfonic acid, followed by 160 mL of ether. The precipitates were collected by filtration, washed with ether and dried to obtain 7.49 g of N-benzyl-t-4-tert-butoxycarbonylamino-4-methyl-r-1-cyclohexylamine p-toluenesulfonate (the compound (4) of the above figure). (5) A mixture comprising 16.63 g of the compound obtained in the above (4), 5.0 g of 10% palladium-carbon and 400 mL of methanol was stirred under hydrogen atmosphere. (1 atm) for 24 hours. 10% palladium-carbon was removed by filtration and the filtrate was concentrated. The resulting residue was dissolved in a mixture of 50 mL of an aqueous 10% sodium-hydroxide solution and 300 mL of ether. The ether layer was washed with water and brine, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure to obtain 6.87 g of t-4-tert-butoxycarbonylamino-4-methyl-r-1-cyclohexylamine (the compound (5) of the above figure). (6) The filtrate in the step of the above (4) was treated with an aqueous sodium hydroxide solution and extracted with chloroform. The extract was washed with water and brine, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure. The residue was applied to NH-silica gel column chromatography (solvent: hexane-ethyl acetate (30:1 to 3:1)) to obtain N-benzyl-c-4-tert-butoxycarbonylamino-4-methyl-r-1-cyclohexylamine. Next, this compound was treated in the same manner as mentioned above (5) to obtain c-4-tert-butoxycarbonylamino-4-methyl-r-1-cyclohexylamine (the compound (6) of the above figure).