[O:1]1[C:10]2[C:5](=[CH:6][CH:7]=[CH:8][CH:9]=2)[CH:4]([OH:11])[CH2:3][CH2:2]1.[N+](=[CH:14][C:15]([O:17][CH2:18][CH3:19])=[O:16])=[N-].Cl[CH2:21]Cl>CCCCCCC.CC(O)=O.CC(O)=O.CC(O)=O.CC(O)=O.[Rh].[Rh]>[CH2:18]([O:17][C:15](=[O:16])[CH2:14][CH2:21][O:11][C:4]1[C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:10]=2[O:1][CH2:2][CH:3]=1)[CH3:19]To a solution of 4-chromanol (1.5 g, 10.0 mmol) in dichloromethane (20 mL) is added rhodium (II) acetate dimer (10 mg) followed by ethyl diazoacetate (0.95 mL, 9.0 mmol). The reaction mixture is stirred at rt for 30 min. The reaction mixture is diluted with heptane, filtered through Celite, and the filtrate is evaporated and the residue purified by chromatography on silica gel; elution with EtOAc:dichloromethane:hexane (10:20:70) gives 1.81 g of the product 475. 1H NMR (CDCl3) δ 7.35 (dd, 1H), 7.22 (dt, 1H), 6.90 (t, 1H), 6.84 (d, 1H), 4.56 (m, 1H), 4.36 (dd, 1H), 4.29 (dd, 1H), 4.23 (q, 2H), 4.19 (s, 2H), 2.18 (m, 1H), 2.05 (m, 1H), 1.30 (t, 3H); MS: m/z 236 (M++1).
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