Azide 10a (0.30 g, 1.9 mmol) was dissolved in methanol (5 mL); then 6N HCl (2 mL) and 10% palladium on charcoal were added to the solution. The resulting mixture was stirred under 1 bar of hydrogen for 3 h, then the catalyst was filtered off, and the solvent was removed under reduced pressure. The residue was dissolvedin 6N HCl (5 mL) and refluxed upon stirring for 1 h, then evaporated in vacuum. The residue was purified by ion-exchange chromatography (Amberlite IR-120(plus) ion-exchange resin, 3.5% aqueous ammonia as an eluent). cis-3-aminocyclobutanecarboxylic acid 1a as white powder, yield 0.16 g, 1.4 mmol, 71%.
