Triethylamine → 7-Boc-9-Cbz-3-oxa-7,9-diazabicyclo[3.3.1]nonane

To a solution of tert-butyl 3-oxa-7,9-diazabicyclo[3.3.1]nonane-7-carboxylate (0.500 g, 2.2 mmol) in dichloromethane (5 ml) was added triethylamine (0.443 g, 4.4 mmol) at room temperature. The mixture was stirred at room temperature for a few mins, and then benzyl chloroformate (0.751 g, 4.4 mmol) was added to the reaction mixture. The resulting mixture was stirred at room temperature overnight. The mixture was partitioned between dichloromethane and water. The organic phase was dried, and concentrated. The residue was purified by silica gel chromatography to give 9-benzyl 7-tert-butyl 3-oxa-7,9-diazabicyclo[3.3.1]nonane-7,9-dicarboxylate 133b (0.637 g, 80.0%). MS: calc'd (MH+) 363, measured (MH+) 363.