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

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Reaction Steps

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 1.0 N 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).

Provenance & Evidence