| 摘要 |
Cyclobutane-1,2-dicarboxylic esters of the formula: (see fig. I) in which R1 is a C1-8-alkyl group, an optionally substituted mono- or bicyclic cycloaliphatic group having 3 to 10 ring carbon atoms, an optionally substituted aryl or arylalkyl group or an optionally substituted saturated heterocyclic group and R2 is either C1-4-alkyl or both radicals R2 together form a group of the formula -(CH2)n- (n = 2 to 4), are prepared from the corresponding maleic or fumaric ester and ketene acetal in the presence of a Lewis acid and a sterically hindered base. The reaction is stereoselective when an optically active maleic or fumaric ester is employed. The cyclobutane-1,2-dicarboxylic esters (I), in particular those having trans configuration, are intermediates in the synthesis of pharmaceutically active compounds.
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