Furan-2 -ones, 4-acetyl-4,5-dihydro

Thermolysis of D-fructose in acid solution provides 11 and 2-(2-hydrox-yacetyl)furan (44) as major products. Earlier work had established the presence of 44 in the product mixtures obtained after acid-catalyzed dehydrations of D-glucose and sucrose. Eleven other products were identified in the D-fructose reaction-mixture, including formic acid, acetic acid, 2-furaldehyde, levulinic acid, 2-acetyl-3-hydroxyfuran (isomaltol), and 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2//)-furanone (59). Acetic acid and formic acid can be formed by an acid-catalyzed decomposition of 2-acetyl-3-hydroxyfuran, whereas levulinic acid is a degradation prod-uct of 11. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one has also been isolated after acid treatment of D-fructose.The pyranone is a dehydration product of the pyranose form of l-deoxy-D-eo f o-2,3-hexodiulose. In aqueous acid seems to be the major reaction product of the pyranone. 

The major products formed from hexoses that react in aqueous acidic solution are 5-(hydroxymethyl)-2-furaldehyde, levulinic acid, and polymeric materials. In addition, many minor dehydration products are found. In a study41 of D-fructose, 2-(2-hydroxyacetyl)furan (13), 2-acetyl-3-hydroxyfuran (isomaltol 16), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, and 3,4,5-trihydroxy-3,5-hexadien-2-one (acetylformoin) were identified. Products not formed solely by dehydration mechanisms include acetone,56 formaldehyde, acetalde-... 

Cyclopropanation products were not isolated from furan and the following diazocarbonyl compounds diethyl 2-diazopent-3-enedioate, ° dimethyl diazomalonate (see also Table 13, entry 9), 6-diazopenicillinates (though not with benzofuran). The carbenoid reaction [copper(II) sulfate, 80 °C] of l-diazopropan-2-one with benzofuran yields 1-acetyl-1 a,6b-dihydro-l//-cyclopropa[ )]benzofuran. ° However, when furan is cyclopropanated with a-di-azo ketones, 6-(l-oxoalkyl)-2-oxabicyclo[3.1.0]hex-3-enes are either not obtained or rearrange slowly even at 20°C to the isomeric 1,4-diacylbuta-l,3-dienes. 

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