[CH3:1][C:2]1([CH3:15])[CH2:13][C:12](=[O:14])[C:5]2[C:6]([C:9](O)=[O:10])=[CH:7][O:8][C:4]=2[CH2:3]1.C(Cl)(=O)C(Cl)=O.[BH4-].[Na+].C([O-])(O)=O.[Na+]>ClCCl.CN(C=O)C.C(OCC)(=O)C.C(O)(=O)C>[CH3:1][C:2]1([CH3:15])[CH2:13][C:12](=[O:14])[C:5]2[C:6]([CH2:9][OH:10])=[CH:7][O:8][C:4]=2[CH2:3]1
6,6-Dimethyl-4-oxo-4,5,6,7-tetrahydro-benzofuran-3-carboxylic acid (17) (1 g, 4.8 mmol) is dissolved in 80 ml dichloromethane and after addition of 187 μl DMF (2.4 mmol) the mixture is cooled to 10-15° C. Oxalylchloride (619 ul, 7.2 mmol) is added drop wise and the mixture is stirred for 30 min at room temperature. The mixture is evaporated under reduced pressure, dissolved in THF and cooled to −55° C. A solution of NaBH4 (1.3 g, 34.1 mmol) in 10 ml of DMF is added via syringe. The white suspension is allowed to stir for another 1.5 h at −55° C. 4 ml of acetic acid is added at this temperature and the mixture is poured into 150 ml of a 5% aqueous NaHCO3 solution. The mixture is diluted with ethyl acetate and washed with brine. The crude product is purified by Flash-chromatography (ethyl acetate/hexanes (4:6), silicagel).
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