Cl[C:2]1(Cl)[C:8](=[O:9])[CH:7]2[CH:3]1[CH2:4][CH:5]=[C:6]2[C:10]([O:12][CH:13]([C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1)[C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11].C(O)(=O)C>O1CCCC1.C(Cl)Cl.[Zn]>[C:14]1([CH:13]([O:12][C:10]([C:6]2[CH:7]3[CH:3]([CH2:4][CH:5]=2)[CH2:2][C:8]3=[O:9])=[O:11])[C:20]2[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=2)[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1To a solution of 50 g of 6,6-dichloro-7-oxobicyclo[3.2.0]hept-2-en-2-carboxylic acid, diphenylmethyl ester, from Example 4, in 75 mL of tetrahydrofuran, was added 500 mL of acetic acid and 100 g of zinc dust. This mixture was stirred mechanically for 6 hr at room temperature and then diluted with 1 L of methylene chloride and filtered. The filtrate was evaporated to a residue which was partitioned between methylene chloride and water. The organic layer was washed with brine, dried over sodium sulfate, and evaporated to give a colorless solid which, when triturated with 150 mL of ether-petroleum ether (1:1), afforded 35.1 g (85.5%) of crystalline 7-oxobicyclo[3.2.0]hept-2-ene-2-carboxylic acid diphenylmethyl ester: IR (Nujol mull): 1625, 1715, 1785 cm-1 ; NMR (220 MHz; CDCl3): δ 2.57 (1H, m), 2.89 (3H, m), 3.27 (1H, m), 4.48 (1H, m), 6.80 (1H, s), 6.86 (1H, m) and 7.1-7.4 (10H, m).
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