To a chilled solution (-70° C.) of 453 mg (2.26 mmol) of the thus obtained 1-(N-methoxy-N-methylcarbamoyl)-5,5-dimethylpyrrolidin-2-one in THF (12 ml) was added 2.26 ml (2.26 mmol) of a THF solution of 1.0M lithium hexamethyldisilazane while being stirred under a nitrogen atmosphere. Five minutes later, 693 mg (2.26 mmol) of 3,5-di-tert-butyl-4-trimethylsiloxybenzaldehyde was added thereto and the mixture was warmed to room temperature and stirred for 2 hours. The reaction mixture was then poured into ice-water and extracted with dichloromethane. The dichloromethane layer was washed with water, dried over magnesium sulfate and evaporated to give a residue, which was then dissolved in 23 ml of toluene. To the mixture was added 145 mg of p-toluenesulfonic acid, which was refluxed for 1.5 hours. The solvent was removed under reduced pressure to give a residue, which was dissolved in 13 ml of THF and stirred under ice-cooling. To the reaction mixture was added 1 ml of a THF solution of 2.0M tetra-n-butylammonium fluoride, which was stirred for 10 minutes. The reaction mixture was poured into ice-water containing sodium bicarbonate and extracted with dichloromethane. The dichloromethane layer was washed with an aq. sodium bicarbonate and water, dried over magnesium sulfate and evaporated to give a residue, which was then chromatographed on silica gel (toluene/ethyl acetate=9/1) and lyophilized from benzene to give 270 mg of the objective compound (Id-3) in 29% yield.
