Chiral Lewis Acid Catalyzed Asymmetric Cycloadditions of Disubstituted Ketenes for the Synthesis of β‑Lactones and δ‑Lactones

Highly
diastereo- and enantioselective [2 + 2]- and [4 + 2]-cycloadditions
of disubstituted ketenes were realized by chiral Lewis acid catalysis.
A series of arylalkylketenes underwent the reaction smoothly with
isatins and β,γ-unsaturated α-ketoesters, providing
optically active β-lactones and δ-lactones with vicinal
chiral centers in excellent yields (up to 99%) and enantioselectivities
(up to 99% ee), as well as exclusively high diastereoselectivities
under 0.2–2 mol % catalyst loading.

本研究通过手性路易斯酸催化，实现了双取代烯酮的高非对映选择性、高对映选择性[2+2]及[4+2]环加成反应。一系列芳基烷基烯酮可与靛红、β,γ-不饱和α-酮酯顺利发生此类环加成反应，在0.2~2 mol%的催化剂负载量下，即可得到含有相邻手性中心的光学活性β-内酯与δ-内酯，产物产率最高可达99%、对映选择性最高达99% ee，且展现出优异专一的非对映选择性。