Padwa Albert, Price Alan T.
Department of Chemistry, Emory University, Atlanta, Georgia 30322.
J Org Chem. 1998 Feb 6;63(3):556-565. doi: 10.1021/jo971424n.
A series of diazo amido keto esters prepared from N-alkenyl-substituted 3-carbalkoxy-2-piperidone derivatives was treated with rhodium(II) acetate. Attack of the amido carbonyl oxygen at the resultant rhodium carbenoid center produced a transient push-pull carbonyl ylide dipole which underwent an intramolecular dipolar cycloaddition reaction. A related annulation sequence was used to prepare the pentacyclic skeleton of the aspidosperma family of alkaloids. Synthesis of the required diazo imide was carried out from 3-carboxy-3-ethyl-2-piperidone and N-methyl-3-indoleacetic acid. Treatment of the diazo imide with rhodium(II) acetate afforded a transient 1,3-dipole which subsequently underwent cycloaddition across the indole pi-bond. The resulting cycloadduct is the consequence of endo cycloaddition with respect to the dipole which is fully in accord with the lowest energy transition state. The cycloadduct was converted in three steps into desacetoxy-4-oxo-6,7-dihydrovindorosine. The stereochemistry of the final product was established by a X-ray crystallographic study.
由N-烯基取代的3-烷氧羰基-2-哌啶酮衍生物制备的一系列重氮酰胺基酮酯用乙酸铑（II）处理。酰胺羰基氧在所得铑卡宾中心的进攻产生了一个瞬态的推挽羰基叶立德偶极子，该偶极子发生了分子内偶极环加成反应。一个相关的环化序列被用于制备阿朴菲类生物碱的五环骨架。所需重氮酰亚胺的合成由3-羧基-3-乙基-2-哌啶酮和N-甲基-3-吲哚乙酸进行。用乙酸铑（II）处理重氮酰亚胺得到一个瞬态1,3-偶极子，该偶极子随后在吲哚π键上进行环加成。所得环加成物是相对于偶极子的内型环加成的结果，这完全符合最低能量过渡态。环加成物经三步转化为去乙酰氧基-4-氧代-6,7-二氢长春罗辛。最终产物的立体化学通过X射线晶体学研究确定。
