Fluoride-Catalyzed [2 + 2] Cycloadditions of Allenoates: Access to Azetidine and Cyclobutene Scaffolds
Jinlong Qian1, Lijin Zhou1, Tingting Chen1
1School of Pharmaceutical and Chemical Engineering & Institute for Advanced Studies, Taizhou University, Taizhou, Zhejiang, 318000, China.
Abstract:
Here, we report fluoride-catalyzed [2 + 2] cycloaddition reactions of allenoates with either imines or alkynoates, affording azetidine and cyclobutene products featuring a highly (E)-selective exocyclic alkene. Mechanistic studies suggest that the high electrophilicity of allenoate enables 1,4-addition of a weakly nucleophilic fluoride catalyst to generate a 3-fluorobutadienolate intermediate, which subsequently undergoes vinylogous addition with the two π-electrophiles. The final step involves a facile intramolecular 1,4-addition/1,2-elimination sequence, releasing the fluoride catalyst and the four-membered cyclic product.
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