Step (i): Synthesis of 5-hydroxy-2-adamantanone (compound of formula 11)
Under cooling in an ice bath, adamantanone (50 g, 333 mmol) was slowly added to concentrated nitric acid (98%, 440 mL) for 15 min while stirring was maintained. The reaction mixture was stirred continuously for 72 h at room temperature and then warmed to 60 °C for 2 h until most of the nitrogen dioxide gas escaped. Excess nitric acid was removed by distillation under reduced pressure and the resulting pale yellow oil solidified on cooling. The reaction mixture was sequentially diluted with deionized water (200 mL) and concentrated sulfuric acid (75 mL), and the resulting clarified yellow solution was heated on a steam bath in a fume hood for 1 hour. The reaction solution was neutralized with 30% aqueous sodium hydroxide under warm conditions and subsequently extracted with chloroform. The organic phases were combined, washed with saturated saline and concentrated under reduced pressure. The crude product was dissolved in dichloromethane (15 mL), hexane was added dropwise until the precipitate was no longer generated, the solid was collected by filtration and dried under vacuum to give 5-hydroxy-2-adamantanone (compound of formula 11, 40.9 g) in 74% yield.
Characterization data:
Melting point: 278.8-300°C;
1H-NMR (CDCl3) δ: 2.69 (bs, 2H), 2.36-2.32 (m, 2H), 2.12-2.02 (m, 2H), 2.02-1.88 (m, 6H), 1.80-1.68 (m, 1H);
IR (cm-1): 3410, 2929, 2855, 2645, 1725, 1539, 1452, 1351, 1288, 1116, 1055, 927, 900, 797;
Mass spectrum (m/z): 167 [M+H]+.
