Regioselective Synthesis of Nitrones by Decarboxylative Oxidation of<i>N</i>-Alkyl-<i>α</i>-amino Acids and Application to the Synthesis of 1-Azabicyclic Alkaloids
作者:Hiroaki Ohtake、Yasushi Imada、Shun-Ichi Murahashi
DOI:10.1246/bcsj.72.2737
日期:1999.12
were prepared by catalytic oxidation of the corresponding chiral pyrrolidines in a regioselective manner. These chiral cyclic nitrones, 17 and 45 are versatile intermediates for the synthesis of optically active nitrogen heterocycles, since stereoselective additions of carbon nucleophiles to these chiral nitrones can be readily performed. Typically, ZnI2-mediated addition of ketene t-butyldimethylsilyl
在相转移条件下用 30% H2O2 溶液钨酸盐催化氧化 N-烷基-α-氨基酸,区域选择性地以良好的产率得到硝酮。使用该方法,实现了(R)-和(S)-4-(叔丁基二甲基甲硅烷氧基)-1-吡咯啉N-氧化物((R)-17a和(S)-17a)的立体发散合成。此外,(R)-和(S)-3-(叔丁基二甲基甲硅烷氧基)-1-吡咯啉N-氧化物((R)-45和(S)-45)是通过相应手性吡咯烷的催化氧化制备的区域选择性方式。这些手性环状硝酮 17 和 45 是合成光学活性氮杂环的通用中间体,因为可以很容易地将碳亲核试剂立体选择性加成到这些手性硝酮上。通常,ZnI2 介导的乙烯酮叔丁基二甲基甲硅烷基甲基缩醛 (29a) 与 (R)-17a 的加成得到顺式加合物,(2R,4R)-[1,4-双(叔丁基二甲基甲硅烷氧基)吡咯烷-2-基]乙酸甲酯(cis-30)。相比之下,将乙炔锂 34 添加到硝酮 (R)-17a 中得到