A new annulation reaction leading to tetrahydropyrans has been discovered. The reaction of homoallylic enol ethers (e.g., 1) with alpha,beta-unsaturated ketones or esters begins with a Mukaiyama-Michael addition. The intermediate oxocarbenium ion undergoes a rapid 2-oxonia-Cope rearrangement, and the resulting zwitterion collapses to form a tetrahydropyran. The reaction is stereoselective with 3-butene-2-one
已经发现了导致
四氢吡喃的新环化反应。高烯丙基烯醇醚(例如,1)与α,β-不饱和酮或酯的反应以向山-迈克尔加成开始。中间体氧碳鎓离子经历了快速的 2-oxonia-Cope 重排,产生的两性离子塌陷形成
四氢吡喃。该反应对 3-butene-2-one 具有立体选择性,但会产生与
丙烯酸乙酯的非对映异构混合物。更复杂的烯酮,如
环己烯酮,也会发生反应以产生稠环产物。底物的旋光性在
四氢吡喃产物中传递。