[C:1]([C:7]1[C:8]([CH3:20])=[C:9]([CH3:19])[C:10]2[O:14][C:13]([C:15]([OH:17])=[O:16])=[CH:12][C:11]=2[CH:18]=1)(=[O:6])[CH2:2][CH:3]([CH3:5])[CH3:4].C=O.Cl.[CH3:24]NC.Cl>CN(C)C=O.C(O)(=O)C>[CH2:24]=[C:2]([CH:3]([CH3:5])[CH3:4])[C:1]([C:7]1[C:8]([CH3:20])=[C:9]([CH3:19])[C:10]2[O:14][C:13]([C:15]([OH:17])=[O:16])=[CH:12][C:11]=2[CH:18]=1)=[O:6]A mixture of 5-isovaleryl-6,7-dimethylbenzofuran-2-carboxylic acid (8.5 g.), paraformaldehyde (2.0 g.), dimethylamine hydrochloride (3.3 g.) and acetic acid (1 ml.) is heated at 95°C. for 2.5 hours, treated with dimethylformamide (75 ml.), heated an additional 3.5 hours, poured into ice water (300 ml.) containing hydrochloric acid (5 ml.). The product is extracted into ether, washed with water, dried over magnesium sulfate, the solvent evaporated at reduced pressure to afford 5-(2-methyleneisovaleryl)-6,7-dimethylbenzofuran-2-carboxylic acid.
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