[Li+].C[Si]([N-][Si](C)(C)C)(C)C.[CH3:11][O:12][CH:13]=[CH:14][C:15](=[O:17])[CH3:16].[CH3:18][C:19]1([C:22](Cl)=[O:23])[CH2:21][CH2:20]1>C1COCC1>[OH:23][C:22]([C:19]1([CH3:18])[CH2:21][CH2:20]1)=[CH:16][C:15](=[O:17])[CH:14]=[CH:13][O:12][CH3:11]LiHMDS (1M in THF, 88 mL, 2 eq) is added dropwise to a cold (−78° C.) solution of 4-methoxy-3-buten-2-one (8.8 mL, 88 mmol, 2 eq) in THF (300 mL). After a 30 min stirring at −78° C., a solution of 1-methyl-cyclopropanecarbonyl chloride (Step 40.8) (5.19 g, 44 mmol) in THF (100 mL) is added. The resulting mixture is allowed to warm to rt over 2 h and quenched by addition of a saturated solution of NH4Cl. THF is removed under vacuum. The concentrated mixture is extracted with Et2O. The organic phase is washed with brine (2×150 mL), dried (Na2SO4), filtered and concentrated. The residue is purified by silica gel column chromatography (Hex/EtOAc, 1:0→95:5) to afford 5.68 g of the title compound as a yellow oil: ESI-MS: 183.1 [M+H]+; TLC: Rf=0.32 (Hex/EtOAc, 9:1).
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