Lewis Base Catalyzed, Sulfenium Ion Initiated Enantioselective, Spiroketalization Cascade.

Kimberly M Hilby, Scott E Denmark

The Journal of organic chemistry 2021 Nov 05

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A Lewis base catalyzed, enantioselective sulfenocyclization of alkenes to afford [6,6]spiroketals has been developed. The method uses a chiral Lewis base catalyst with an electrophilic sulfur source to generate enantioenriched thiiranium ion with alkenes. Upon formation, the thiiranium ion is subsequently captured in a cascade-type reaction, wherein a ketone oxygen serves as the nucleophile to open the thiiranium ion and an alcohol provides the secondary cyclization to form biorelevant spiroketals. A variety of electron-rich and electron-neutral E-substituted styrenes form the desired spiroketals in good yields with excellent enantio- and diastereoselectivities. Alkyl-substituted and terminal alkenes participate in the cascade reaction, but with a limited scope compared to the styrenyl substrates. This method allows for rapid formation of highly substituted spiroketals in good yield and excellent enantioselectivity.

Citation

Kimberly M Hilby, Scott E Denmark. Lewis Base Catalyzed, Sulfenium Ion Initiated Enantioselective, Spiroketalization Cascade. The Journal of organic chemistry. 2021 Nov 05;86(21):14250-14289