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在L-脯氨酸催化的芳香醛与丙酮直接不对称aldol反应体系中添加二醇或二酚类助剂可有效提高反应活性.助剂的使用降低了该反应体系中L-脯氨酸的用量.特别是以邻苯二酚为助剂时,最佳反应条件下,仅用5mol%L-脯氨酸与1mol%助剂催化2-硝基苯甲醛与丙酮直接不对称aldol反应,aldol产物产率高达90%,对映选择性为80%.该反应产率比未加助剂条件下,L-脯氨酸用量为30mol%时的反应产率高.采用量子化学计算研究了助剂对该反应的促进作用.结果表明,助剂可与芳香醛的醛基形成氢键,从而活化醛基,提高反应效率.邻苯二酚结构中相邻的羟基能与底物芳香醛羰基的氧原子形成双氢键,大大活化了底物芳香醛的羰基.因此,该助剂可有效促进L-脯氨酸催化剂的直接不对称aldol反应.
In the L-proline-catalyzed aldehydes and acetone direct asymmetric aldol reaction system to add diol or diphenol auxiliaries can effectively improve the reactivity.The use of additives to reduce the L-proline in the reaction system Especially with catechol as assistant, under the optimal reaction conditions, only 5mol% L-proline and 1mol% promoter catalyzed the direct asymmetric aldol reaction between 2-nitrobenzaldehyde and acetone, aldol The yield of the product was as high as 90%, and the enantioselectivity was 80% .The reaction yield was higher than that without adding auxiliaries, when the amount of L-proline was 30mol% .The quantum chemical calculation Agent on the reaction.The results show that the auxiliary agent can form hydrogen bond with the aldehyde group of the aromatic aldehyde to activate the aldehyde group and improve the reaction efficiency.The adjacent hydroxyl groups in the catechol structure can react with the substrate aromatic aldehyde carbonyl Of the oxygen atoms to form a double hydrogen bond, greatly activated the carbonyl carbonyls of the substrate aromatic aldehyde, therefore, the additive can effectively promote the direct asymmetric aldol reaction of the L-proline catalyst.