S(=O)(=O)(O)O.[CH3:6][C:7](=[CH:13][CH:14]([O:17][CH3:18])[O:15][CH3:16])[CH:8]([O:11][CH3:12])[O:9]C.C([O-])(O)=O.[Na+]>O>[CH3:6]/[C:7](=[CH:13]\[CH:14]([O:17][CH3:18])[O:15][CH3:16])/[CH:8]=[O:9].[CH3:6][C:7](=[CH:13][CH:14]=[O:15])[CH:8]=[O:9].[CH3:6][C:7]1[CH:8]([O:11][CH3:12])[O:17][CH:14]([O:15][CH3:16])[CH:13]=1A solution of 0.2 g of concentrated sulfuric acid and 1 g of water in 9.5 of 2-methyl-1,1,4,4-tetramethoxybut-2-ene was stirred for 0.5 h at RT. The sulfuric acid was neutralized with solid NaHCO3, after which the mixture was filtered. The filtrate was worked up by distillation in an Allihn apparatus (150° C./20 mbar), 0.8 g of residue and 4.8 g of distillate being obtained. Gas chromatographic analysis gave 55.6% of (E)-2-methyl-4,4-dimethoxybut-2-enal, 2.9% of 2-methylbut-2-ene-1,4-dial, 18.8% of 3-methyl-2,5-dimethoxy-2,5-dihydrofuran and 8.2% of unconverted starting material.
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