[C:1]([O:5][C:6](=[O:15])[NH:7][C:8]1[S:9][C:10]([CH2:13][OH:14])=[CH:11][N:12]=1)([CH3:4])([CH3:3])[CH3:2].C1C=C[NH+]=CC=1.C1C=C[NH+]=CC=1.[O-][Cr](O[Cr]([O-])(=O)=O)(=O)=O.C1COCC1>ClCCl>[C:1]([O:5][C:6](=[O:15])[NH:7][C:8]1[S:9][C:10]([CH:13]=[O:14])=[CH:11][N:12]=1)([CH3:4])([CH3:2])[CH3:3]To a solution of compound 62.2 (18.5 mmol) in dichloromethane is added molecular sieves (4.0 g) and PDC (39.0 mmol) at room temperature (THF is added to help dissolve the starting material). After 1.5 hours, an additional equivalent of PDC is added and the reaction is stirred for 5.5 hours. The reaction mixture is poured directly onto a silica gel column and is eluted with a gradient of 100% dichloromethane to 100% EtOAc. Fractions containing the desired product are pooled and concentrated to afford (5-formyl-thiazol-2-yl)-carbamic acid tert-butyl ester (compound 62.3).
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