C(O[C:6](=[O:18])[C:7]1[CH:12]=[CH:11][C:10]([CH2:13][CH3:14])=[C:9]([N+:15]([O-:17])=[O:16])[CH:8]=1)(C)(C)C.C=O.[CH3:21][C:22]([CH3:25])([O-:24])[CH3:23].[K+].CCCCCC.C[CH2:34][O:35]C(C)=O>CS(C)=O.C(Cl)Cl>[C:22]([O:24][C:6]([C:7]1[CH:12]=[CH:11][C:10]([CH:13]([CH3:14])[CH2:34][OH:35])=[C:9]([N+:15]([O-:17])=[O:16])[CH:8]=1)=[O:18])([CH3:25])([CH3:23])[CH3:21]
To a suspension of 4-ethyl-3-nitrobenzoic acid tert-butyl ester (11e) (10 g, 40 mmol) and paraformaldehyde (1.8 g, 60 mmol) in DMSO (10 mL) was added in portions potassium tert-butoxide (590 mg, 5.8 mmol), during which the colour of the reaction mixture was changing from yellow to purple. After stirring for 1 hour at room temperature, the reaction mixture was suspended in CH2Cl2, adsorbed onto silica gel (15 g) in vacuo and purified by flash chromatography (100 g silica, column: 3.5×14 cm, solvent: hexane/EA 3:1). The product was obtained as a yellow oil in 94% yield (10.57 g, 38 mmol). Rf=0.34 (hexane/EtOAc 3:1). 1H NMR (250 MHz, CDCl3) δ 8.27 (d, 1H, arom. H(3)), 7.58 (dd, 1H, arom. H(5)), 7.53 (d, 1H, arom. H(6)), 3.76 (m, 2H, α-CH2), 3.50 (sextet, 1H, β-CH), 1.81 (t, 1H, OH), 1.57 (s, 9H, 3×CH3 COOtBu), 1.31 (d, 3H, CH3).
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