tert-butyl 3-oxo-2-oxa-5-azabicyclo[2.2.1]heptane-5-carboxylate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a solution of 1-tert-butyl 2-methyl (2S,4R)-4-hydroxypyrrolidine-1,2-dicarboxylate (170.0 g, 0.736 mol) and PPh3 (237.0 g, 0.88 mol) in dry THF (1.5 L) was added dropwise DIAD (178.35 g, 0.88 mol) at 0° C. under N2 gas. After addition, the resulting reaction mixture was stirred at room temperature overnight. TLC (petroleum ether/EtOAc 3:1) indicated the complete consumption of compound 1A. The solvent was removed in vacuo. The residue was purified by column chromatography (silica gel, petroleum ether/EtOAc 6:1) which gave the title compound IVa as a white solid (110.0 g, yield: 72.0%). After addition the resulting reaction mixture the complete consumption of compound 1A The solvent was removed in vacuo The residue was purified by column chromatography (silica gel, petroleum ether/EtOAc 6:1) which