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

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posted on 03.01.2014, 00:00 by Xiaoyu Hao, Xiaohua Liu, Wei Li, Fei Tan, Yangyang Chu, Xiaohu Zhao, Lili Lin, Xiaoming Feng
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.