To a solution of N-(4-bromobenzyl)-N,N-diisopropylamine (2.3 g) in THF (10 ml) was added dropwise at −78° C. n-BuLi (1.6 mmol/ml hexane solution, 3.8 ml). Ten minutes later, N,O-dimethyl-N-(1-trityl-piperidine-4-carbonyl)hydroxylamine (1.5 g) in THF (20 ml) was added dropwise to the mixture, and the mixture was stirred at the same temperature for 30 minutes. To the mixture was added ammonium chloride aqueous solution, and the mixture was extracted with ethyl acetate. The extract was washed with water, dried (MgSO4) and concentrated to give the title compound (5.0 g).
