Dimethyl Sulfate → (S)-(+)-2-ethynyl-3,4-dihydro-6-methoxy-2,5,7,8-tetramethyl-2H-1-benzopyran

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A solution of (S)-(+)-2-ethynyl-3,4-dihydro-2,5,7,8-tetramethyl-2H-1-benzopyran-6-ol (354 mg, 1.54 mmol) in acetone (9 mL) was treated with dimethyl sulfate (0.8 mL), and 50% NaOH (1.2 mL) for 2 h at 25° C. with stirring. Ammonium hydroxide solution (1.0N, 50 mL) was added, and it was extracted with ether (3×50 mL). The extracts were combined, washed with 1.0N HCl, water, and dried over MgSO4. It was filtered and concentrated in vacuo to give 400 mg of solid, which or crystallization from ether-hexane (1:12) afforded 141 mg (47%) of (S)-(+)-2-ethynyl-3,4-dihydro-6-methoxy-2,5,7,8-tetramethyl-2H-1-benzopyran as white prisms: mp 94°-97° C., [α]D25 +53.86°, (C 0.4233, CHCl3).

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