作者:Lingjiang Cheng、David A. Lightner
DOI:10.1055/s-1999-3669
日期:——
Regioselective synthesis of α-cyanopyrroles (vs. α-alkoxycarbonylpyrroles) using oximinocyanoacetate esters in a Knorr-type reductive condensation with β-diketones can be directed by the presence of water. Thus, methyl oximinocyanoacetate was reacted with pentane-2,4-dione in hot acetic acid in the presence of zinc dust to give exclusively 3,5-dimethylpyrrole-2-carbonitrile when the acetic acid was wet; whereas, in glacial acetic acid only methyl 3,5-dimethylpyrrole-2-carboxylate was isolated (∼40% yield).
水存在下的区域选择性合成:利用Knorr型还原缩合反应,通过肟基氰基乙酸乙酯与β-二酮反应,可定向生成α-氰基吡咯(而非α-烷氧羰基吡咯)。例如,在锌粉存在的条件下,将甲基肟基氰基乙酸乙酯与戊烷-2,4-二酮在热的含水乙酸中反应,可专一性地得到3,5-二甲基吡咯-2-碳腈;而在冰醋酸中反应时,仅能分离出甲基3,5-二甲基吡咯-2-羧酸酯(约40%产率)。