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Stereo- and Regioselective Synthesis of Molecular Baskets
- Gunther, Michael J., Pavlović, Radoslav Z., Fernandez, Joseph P., Zhiquan, Lei, Gallucci, Judith, Hadad, Christopher M., Badjić, Jovica D.
- Journal of organic chemistry 2019 v.84 no.7 pp. 4392-4401
- bromination, catalysts, copper, diastereomers, fumarates, nanomaterials, organic chemistry, regioselectivity, stereoselectivity
- We describe a stereoselective method for obtaining multigram quantities of molecular basket 1ₛyₙ in overall 11% yield, using inexpensive cyclopentadiene and diethyl fumarate as starting materials. First, an asymmetric synthesis of enantioenriched bromo(trimethylstannyl)alkene (−)-8 was accomplished by the stereoselective bromination of dibromonorbornene (+)-4 guided by anchimeric assistance and subsequent syn-exo-elimination of tetrabromonorbornane (−)-5a as the key steps. Subsequent Cu(I)-catalyzed cyclotrimerization of (−)-8 was optimized to give 1ₛyₙ/ₐₙₜᵢ in 85% yield and 1:1 ratio of diastereomers. Importantly, the results of our mechanistic experiments were in line with the cyclotrimerization occurring in a chain-type fashion with racemization of a Cu(I) homochiral dimeric intermediate, reducing the stereoselectivity of the transformation. Enabled by more facile access to molecular baskets of type 1ₛyₙ, a range of recognition studies can now be completed for producing novel supramolecular catalysts, organophosphorus scavengers, and nanostructured materials.