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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.