Br[C:2]1[CH:3]=[CH:4][C:5]2[O:10][C:9]([CH3:12])([CH3:11])[O:8][CH2:7][C:6]=2[CH:13]=1.C([Li])CCC.CN(OC)[C:21](=[O:23])[CH3:22]>C1COCC1.C(OCC)(=O)C>[C:21]([C:2]1[CH:3]=[CH:4][C:5]2[O:10][C:9]([CH3:12])([CH3:11])[O:8][CH2:7][C:6]=2[CH:13]=1)(=[O:23])[CH3:22]To the product of step (a) (110 g, 0.46 mol) in 1.0 L of THF at −78° C. was added 236 mL (0.51 mol) of 2.14 M n-butyllithium in hexanes via a dropping funnel. After 30 minutes, N-methyl-N-methoxy acetamide (71 g, 0.69 mol, available from TCI) was added. After 2 hours, the reaction mixture was quenched with water, diluted with 2.0 L of 1.0 M aqueous phosphate buffer (pH=7.0) and extracted once with diethyl ether. The diethyl ether phase was washed once with brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give a light orange oil. The oil was dissolved in a minimum volume of ethyl acetate, diluted with hexanes, and to give the title compound as a crystalline solid.
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