Reaction Steps
To a suspension of compound 7b (304 mg, 1 mmol) in 2-butanone (13 mL) and DMF (1.3 mL) was added potassium carbonate (346 mg, 2.5 mmol), 3-chloro-3-methyl-1-butyne (0.56 mL, 5 mmol) and tetrabutylammonium iodide (360 mg, 1 mmol). The reaction mixture was heated to 60° C. for 1 h, then anhydrous ZnCl2 (1.0 M solution in ether, 1.3 mL) was added. The reaction mixture was heated to 70° C. for 26 h, then cooled to r.t., quenched with saturated aqueous NH4Cl (25 mL), and extracted with ethyl acetate (2×75 mL). The organic solutions were combined, washed with brine, dried (Na2SO4), and concentrated. The crude product obtained was purified by silica gel chromatography (8:1 hexane/ethyl acetate) to obtain 5b as a yellow solid (270 mg, 73%). mp: 65-68° C.; Rf: 0.54 (4:1 hexane/ethyl acetate); 1H NMR (CDCl3) 1.04 (3H, d, J=7.2 Hz), 1.39 (9H, s), 1.52 (6H, s), 1.66-1.71 (2H, m), 2.90 (2H, t, J=7.8 Hz), 5.62 (1H, d, J=10.2 Hz), 6.07 (1H, s), 6.30 (1H, d, J=10.2 Hz), 6.62 (1H, s); 13C NMR (CDC13) 13.8, 22.9, 26.9, 27.8, 38.3, 39.3, 78.1, 103.5, 107.9, 110.9, 113.4, 115.9, 129.1, 148.9, 152.0, 155.1, 157.4, 160.6, 176.2; IR (film): 2967, 1750, 1616, 1364, 1142 cm−1; MS m/e 371 (M+1); Anal. Calcd. for C22H26O5: C, 71.33; H, 7.07. Found: C, 71.08; H, 7.35.
