tert-butyl 2-oxo-3a,4,6,6a-tetrahydro-3H-pyrrolo[3,4-d][1,3]oxazole-5-carboxylate

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

Procedure: A solution of tert-butyl 3-[(tert-butoxycarbonyl)amino]-4-[(methylsulfonyl)oxy]pyrrolidine-1-carboxylate (850 mg) in dichloroethane (50 mL) was refluxed overnight, evaporated and the resulting residue purified on a Biotage Horizon® system (silica, gradient 10-15% methanol in dichloromethane) to yield a racemic mixture of tert-butyl 2-oxohexahydro-5H-pyrrolo[3,4-d][1,3]oxazole-5-carboxylate which was resolved by chiral HPLC (Chiralcel OJ column, isopropyl alcohol/hexptane 13:87) to yield fast moving isomer A and slow moving isomer B. Each of isomer A and isomer B was treated with trifluoroacetic acid/methylene chloride (1:1) and passed through ion exchange resin (Strata-X-C™) and eluted with methanol containing 5% ammonium hydroxide to yield hexahydro-2H-pyrrolo[3,4-d][1,3]oxazol-2-one isomer A2 and isomer B2, respectively. evaporated the resulting residue purified on a Biotage Horizon® system (silica, gradient 10-15% methanol in dichloromethane) to yield to yield fast eluted with methanol containing 5% ammonium hydroxide