tert-butyl 5-(3-nitropyridin-4-yl)-2-oxo-3a,6,7,7a-tetrahydrobenzo[d]oxazole-3(2H)-carboxylate → tert-butyl 5-(3-aminopyridin-4-yl)-2-oxohexahydrobenzo[d]oxazole-3(2H)-carboxylate

To a solution of (+/−)-tert-butyl 5-(3-nitropyridin-4-yl)-2-oxo-3a,6,7,7a-tetrahydrobenzo[d]oxazole-3(2H)-carboxylate (1.0 equiv.) in methanol and ethyl acetate (1:1, 0.1 M) was added 10% Pd/C (0.1 equiv.). The resulting mixture was stirred under H2 atmosphere for 6 hours. The solid was removed by filtration. The filtrate was concentrated under reduced pressure to give (+/−)-tert-butyl 5-(3-aminopyridin-4-yl)-2-oxohexahydrobenzo[d]oxazole-3(2H)-carboxylate (87%), which was used in the next step without further purification. LC/MS (m/z): MH+=334.1, Rt=0.51.