Cycloaddition Reaction of Mesoionic Betaines as an Approach toward Trialkylindoline Alkaloids
作者:Albert Padwa、Scott R. Harring、Mark A. Semones
DOI:10.1021/jo970847m
日期:1998.1.1
cross-conjugated heteroaromatic betaine. This 1,4-dipole undergoes a subsequent intramolecular dipolar cycloaddition across the neighboring pi-bond, and the resulting cycloadduct is subsequently converted to the annulated lactam. A related annulation sequence leading to a key intermediate previously utilized in the synthesis of the (+/-)-vallesamidine has been developed which is based on the intramolecular dipolar
跨束缚的吲哚π键上的脱水-4-羟基-2-氧-2-氧-1,3-噻嗪氢氧化物的分子内1,4-偶极环加成已用于构建epi-16,17-dihydroeburnamenine的五环骨架。3-乙基-3-(烯基)哌啶酮与二烯酮和三氟甲磺酸三甲基甲硅烷基酯在环境温度下的苯反应生成环吡啶酮,收率很高。最初的反应涉及形成N-乙酰乙酰基酰胺,然后用TMSOTf将其进一步转化为吡啶酮。发现整个过程以完全的立体特异性进行。用双烯酮和TMSOTf处理3-乙基-3-[((E)-4-苯基-3-丁烯基] -2-哌啶酮)样品可产生63%收率的环加成物,其立体化学通过X射线晶体学研究得以阐明。该差向异构体Z-异构体产生了环化二氢吡啶酮的不同立体异构体。环化的机理涉及TMSOTf诱导的环化,然后去除质子并产生交叉缀合的杂芳族甜菜碱。该1,4-偶极分子经过相邻的π键进行分子内偶极分子环加成反应,然后将所得的环加合物转化为环状内酰