[N:1]12[C:7](=[O:8])[CH2:6][CH:5]1[CH2:4][C:3](=[O:9])[CH:2]2[C:10]([O:12][CH2:13][C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11].S(OC)(O[CH3:24])(=O)=O.[H-].[Na+]>CN(C)P(N(C)C)(N(C)C)=O>[CH3:24][O:9][C:3]1[CH2:4][CH:5]2[N:1]([C:7](=[O:8])[CH2:6]2)[C:2]=1[C:10]([O:12][CH2:13][C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11]A solution of benzyl 1-azabicyclo[3.2.0]heptan-3,7-dione-2-carboxylate (25.9 mg, 0.1 mMol) in anhydrous hexamethylphosphoramide (1.0 ml) is cooled in an ice-bath and stirred under a nitrogen atmosphere. Dimethyl sulfate (11.4 μl, 0.12 mMol) and 57% sodium hydride in mineral oil (5.0 mg, 0.12 mMol) are added to the solution. The cooling bath is removed and the resulting mixture is stirred at room temperature for 60 minutes. The mixture is diluted with ethyl acetate (10 ml) and water (20 ml), shaken, and the layers separated. The organic layer is washed with water (3×5 ml) and brine, dried with magnesium sulfate, diluted with toluene (10 ml), and evaporated under vacuum to an oil. This material is chromatographed on a 0.25 mm×10×20 cm silica gel GF plate using 3:1 toluene-ethyl acetate as developing solvent. The major UV visible band at Rf 0.1 was removed and eluted with ethyl acetate to provide benzyl 3 -methoxy-1-azabicyclo[3.2.0]hept-2-en-7-one-2-carboxylate (5.6 mg) as a clear oil: IR (CH2Cl2) 1775 and 1700 cm-1 ; UV (EtOAc) 288 nm; NMR (CDCl3) δ2.87 (dd, 1, J=2.8 and 16, H6β), 3.03 (m, 2, H4a and H4b), 3.50 (dd, 1, J=5.5 and 16, H6α), 3.80 (m, 1, H5), 3.92 (s, 3, CH3), 5.28 (s, 2, CH2 φ), and 7.40 (m, 5, C6H5); mass spectrum m/e 273 (M+) and 231 (M+-42).
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