[OH:1][CH:2]([C:12]1[CH:17]=[CH:16][C:15]([S:18][CH3:19])=[CH:14][CH:13]=1)[C:3]([C:5]1[CH:10]=[CH:9][CH:8]=[C:7]([CH3:11])[CH:6]=1)=[O:4].[Bi]=O>C(O)(=O)C>[CH3:11][C:7]1[CH:6]=[C:5]([C:3](=[O:4])[C:2]([C:12]2[CH:13]=[CH:14][C:15]([S:18][CH3:19])=[CH:16][CH:17]=2)=[O:1])[CH:10]=[CH:9][CH:8]=1The ketone from step 2 (30.5 mmol, 8.31 g) was diluted with acetic acid (90 ml) and heated to ˜90° C. Bi2O3 (30.5 mmol, 14.2 g) was added. After stirring 15 minutes, additional bismuth oxide (15 mmol, 7 g) was added. After 30 additional minutes, the mixture was filtered through silica and Celite®, then lyophilized. The residue was subjected to chromatography (3:1 hexane: ethyl acetate), affording the title compound as a yellow solid (3.56 g, 43%), which was used in the next step.
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