To a solution of 2-((3S)-4-{[tert-butyl(dimethyl)silyl]oxy}-3-hydroxybutyl)-6-methoxyphenol (6.90 g, 21.1 mmol) in toluene (250 mL) cooled to 0° C. is added triphenylphosphine (6.10 g, 23.2 mmol) followed by dropwise addition of diethyl azodicarboxylate (4.05 g, 23.2 mmol). The reaction mixture is allowed to stir at room temperature for 15 min. The reaction-mixture is quenched by the addition of water (300 mL). The aqueous layer is separated and extracted with diethyl ether (2×150 mL). The combined organic extracts are washed with water (200 mL), aqueous sodium chloride (300 mL), dried (magnesium sulfate) and the solvent is removed in vacuo to give a crude oil. Purification by flash column chromatography (silica, ethyl acetate:hexanes 1:4) provided 4.94 g (76%, 40% ee) of tert-butyl(dimethyl)silyl [(2R)-8-methoxy-3,4-dihydro-2H-chromen-2-yl]methyl ether as a colorless oil. [α]D25=−25.84 (c 10.82 in chloroform, 40% ee); Rf=0.68 (silica, ethyl acetate:hexanes 1:4); Anal. Calcd. for C17H28O3Si.0.1H2O: C, 65.8; H, 9.16. Found: C, 65.75; H, 8.88.
