Oxathiaborolium-Catalyzed Enantioselective [4 + 2] Cycloaddition and Its Application in Lewis Acid Coordinated and
Ramalingam Boobalan1, Rong-Jie Chein1
1Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan.
Abstract:
The nascency of second-generation sulfur-stabilized borenium cations by halophilic Lewis acid SnCl4 leads to highly active chiral Lewis acids that are very effective catalysts for [4 + 2] cycloaddition. Oxathiaborolium pentachlorostannate (5-10 mol %) successfully catalyzed cycloaddition of various dienes and dienophiles to afford cycloadducts with excellent enantioselectivity (20 examples, up to 99% ee). This super Lewis acid also exhibited good enantioselectivity for the first Lewis acid coordinated and chiral Lewis acid catalyzed [4 + 2] cycloaddition to α,β-unsaturated mixed ester amide.
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