[C:1]([O:9][CH:10]1[CH2:13][N:12]([C:14]2[O:15][CH2:16][CH:17]([C:19]([O:21][CH3:22])=[O:20])[N:18]=2)[CH2:11]1)(=[O:8])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C(#N)C>C1(C)C=CC=CC=1.C(Cl)Cl.[O-2].[O-2].[Mn+4]>[C:1]([O:9][CH:10]1[CH2:13][N:12]([C:14]2[O:15][CH:16]=[C:17]([C:19]([O:21][CH3:22])=[O:20])[N:18]=2)[CH2:11]1)(=[O:8])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1
To a solution of 3-benzoyloxy-1-(4-methoxycarbonyl-1,3-oxazolin-2-yl)azetidine (9.12 g, 30.0 mmol) (obtained as described in Reference Example 70(5)) in a mixture of toluene (450 ml) and methylene chloride (180 ml) was added manganese dioxide (63.8 g) and the mixture was heated under reflux for 5 hours. After checking the completion of the reaction, the mixture was filtered and the filtrate concentrated under reduced pressure. The residue was purified by chromatography on a silica gel column using toluene:acetonitrile=1:1 as the eluant to afford 3-benzoyloxy-1-(4-methoxycarbonyl-1,3-oxazol-2-yl)azetidine (5.24 g, yield 58%) as pale yellow crystals.
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