2-oxonia Cope rearrangement is shown to play an important role in Lewis acid-induced π-cyclization reactions of a variety of methyl 2-acetoxy-2-(3-alken-1-oxy)acetates to 5- and 6-membered ring ethers. The influence of this [3,3]-sigmatropic rearrangement on the regio- and stereochemical outcome of the cyclization is evaluated by studying three types of substrates, namely (1) four chain-substituted precursors
研究表明,2-氧代
戊二烯Cope重排在
路易斯酸诱导的各种2-乙酰氧基-2-(3-烯-1-氧基)
甲基丙烯酸酯生成5-和6-元的π-环化反应中起重要作用。
环醚。通过研究三种类型的底物,即(1)四个链取代的前体,(2)三个
硅取代的前体(烯丙基和
乙烯基硅烷)和(3)两种对映纯前体。控制因素是π-亲核试剂的性质和氧碳鎓离子中间体的取代方式。绝对立体
化学保留在对映体纯底物的环化中。