C([C:5]([O:7][CH2:8]CC(O)C)=[O:6])(C)(C)C.[C:13]1([OH:19])[CH:18]=[CH:17][CH:16]=[CH:15]C=1.C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1.N(C(OCC)=O)=NC(OCC)=O>C1COCC1>[CH3:8][O:7][CH2:5][O:6][C@@H:16]1[CH2:15][C@@H:13]([OH:19])[CH:18]=[CH:17]1To a solution of 3.47 g (19.9 mmol) of alcohol 25 (prepared in 30-(1)), 2.81 g (29.9 mmol) of phenol, and 7.88 g (29.9 mmol) of triphenylphosphine in 100 ml of dry THF is added a solution of 4.65 ml of diethyl azodicarboxylate in 40 ml of dry THF dropwise under ice cooling. After additional stirring at the same temperature for 20 minutes, the mixture is stirred for further 2 and half hours. The reaction mixture is concentrated under reduced pressure and the residue is purified by column chromatography on silica gel (200 g of silica gel, ethyl acetate:n-hexane=1:49 to 1:19) to give 4.35 g of the desired phenyl ether 3 as an oil in 87.4% yield.
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