ビス（トリフルオロメチル）ケテンと活性オレフィンとの反応におけるシクロブタノン生成の機構

概要

論文の詳細を見る
Ketenes undergo cycloaddition most readily with an activated olefin (2π system), such as vinyl ethers, to give cyclobutanone. The cyclobutanone formation pathway has not been settled yet. The reactions have long been regarded to be of two steps including a zwitterionic intermediate. Proofs of a zwitterion intermediate were neither detected nor quenched. Selecting two reactants and choosing experimental conditions precisely, we have made low-temperature experiments of the reaction. Low-temperature NMR experiments have proved that the key initial intermediate of the reaction is a [2 + 2]-type cycloadduct, α-methyleneoxetane (not a zwitterion), which ring-cleaves to a transient intermediate 1,4-zwitterion on warming converting a [2 + 2]-type cycloadduct cyclobutanone eventually. We have succeeded in obtaining a direct spectroscopic evidence of short-lived zwitterion for the first time by low-temperature UV-visible experiments. The 1,4-zwitterion was also quenched with acetone on warming to afford 1,4-dipolar cycloadducts indicating a further evidence of the existence of the zwitterions after the formation of α-methyleneoxetane. Theoretical calculations have also resulted that the reaction should proceed in the same way.
基礎有機化学会（基礎有機化学連合討論会）の論文