Pyridine → 2-Aza-spiro[4.5]decane-2,4-dicarboxylic acid 2-benzyl ester 4-methyl ester

A solution of (4) (3 g; 10.44 mmol) and 10% Pd (OH)2/C (0.60 g; 20% w/w) in methanol (50 mL) was stirred for 24 hours at 40° C. under at atmosphere of dry hydrogen gas. The catalyst was filtered off through a celite pad, and the filtrate was concentrated in vacuo to give 2 g (10.14 mmol; 97%) of (5) as a colorless oil which was used without any further purification. To a solution of (5) (2 g; 10.14 mmol) in dry dichloromethane (100 mL) was successively added, at 0° C., under an argon atmosphere, pyridine (2.04 mL; 25.35 mmol), and benzylchloroformate (2.89 mL; 20.24 mmol). The reaction mixture was then allowed to stir at room temperature for 2 days. The reaction mixture was washed (2×50 mL) with 1N HCl, dried over MgSO4, and concentrated in vacuo. The crude oil was purified by silica-gel flash chromatography in ether/heptane (1:1) to give 2.97 g (8.96 mmol; 88%) of (6) as a colorless oil.