Tandem Dipolar Cycloaddition−Mannich Cyclization as an Approach to Tricyclic Nitrogen Heterocycles
作者:Albert Padwa、Michael A. Brodney、Joseph P. Marino、Martin H. Osterhout、Alan T. Price
DOI:10.1021/jo9607267
日期:1997.1.1
stereochemistry of the resulting A/B ring fusion is analogous to similar erythrinane products obtained via a Mondon-enamide-type cyclization. The stereochemical assignment of the final cyclized products was determined by X-ray crystallography. Molecular mechanics calculations show that the ground state energy of the cis-fused diastereomer is 4.6 kcal lower than that of the trans diastereomer, and presumably some
制备了一系列2-重氮-N- [2-(3,4-二甲氧基苯基)乙基] -N-庚-6-烯酰基丙二酰胺,并用催化量的全氟丁酸铑(II)处理。生成的类胡萝卜素在邻近的酰胺羰基氧原子上进行容易的环化反应,生成异麦草酮型中间体。随后通过侧链烯烃的1,3-偶极环加成以高收率提供分子内环加合物。这些环加合物暴露于三氟化硼醚化物会导致路易斯酸诱导的开环,生成N-酰基亚胺离子,然后将其进行曼尼希环化作用,使其与酰胺氮原子相连的相邻pi骨架上。所得A / B环稠合的顺式立体化学类似于通过蒙登-烯酰胺型环化获得的类似赤藓烷产物。最终环化产物的立体化学分配通过X射线晶体学测定。分子力学计算表明,顺式稠合非对映异构体的基态能量比反式非对映异构体的基态能量低4.6 kcal,据推测,部分热力学能差反映在环化的过渡态中。在某些情况下,最初形成的N-酰基亚胺离子的质子损失发生在环化之前,以产生酰基酰胺,随后将其酰胺化,产生表