tert-Butanol → [5-Oxo-1-(3-oxo-3,4-dihydro-2H-1,4-benzoxazin-6-yl)pyrrolidin-3-yl]carbamic acid tert-butyl ester

A mixture of 5-oxo-1-(3-oxo-3,4-dihydro-2H-1,4-benzoxazin-6-yl)pyrrolidin-3-carboxylic acid (300 mg, 1.09 mmol), diphenyl phosphoryl azide (351 μl, 1.63 mmol), triethylamine (380 μl, 2.73 mmol) and tert-butyl alcohol (10 ml) was heated under reflux for 24 hours. The reaction solution was cooled, the solvent was then removed under reduced pressure, and the obtained residue was suspended in ethyl acetate to collect the insoluble material by filtration. The obtained residue was purified by silica gel column chromatography (chloroform/methanol) to yield 230 mg (61%) of the title compound in the form of a colorless solid.