| 摘要 |
<p>NEW MATERIAL:A 4H pyran of formula I (R<1> is H, alkyl, alkenyl, cycloalkyl, aralkyl or acyl; R<2>, R<3> and R<4> are H, alkyl, alkenyl, aryl, cycloalkyl or aralkyl). EXAMPLE:5-Ethyl-6-hydroxy-2,3-dimethoxycarbonyl-5,6-dihydro-4H-pyran. USE:Useful as an intermediate for synthesizing pyridine-2,3-dicarboxylic acids which are intermediates for herbicides: 2-(2-imidazoline-2-yl)pyridines. PREPARATION:A compound of formula II (R<5> and R<6> are alkyl, alkenyl, cycloalkyl, etc., or acetal type protecting groups which forms together an alkylene group) is hydrolyzed in the presence of an acid to provide the compound of formula I.</p> |
