We have developed a Cu(II)-catalyzed spiroannulation of allylsilanes with <i>N</i>-Boc-iminooxindoles to yield spirocarbamate oxindoles. This reaction proceeds in high yield and diastereoselectivity. An enantioselective variant, which proceeds with excellent selectivity, has been developed in tandem with mechanistic studies to obtain information about the catalyst complex. The rate of reaction and overall conversion is greatly enhanced by essential additive sodium tetrakis[(3,5-trifluoromethyl)phenyl]borate (NaBArF).  Electron paramagnetic resonance (EPR) is used to study the Cu(II) complex, assessing the role of chiral ligand, additive NaBArF, and water in the enantioselective reaction. Catalytically active copper species are identified by EPR and correlated with experimental data. A significant nonlinear effect is observed, indicating agglomeration of the Cu(II) catalyst complex is a key factor for reactivity and selectivity. This study not only sheds light on the allylsilane addition reaction and highlights EPR as a useful technique to study this system, but also provides valuable information about the Cu(II)-Box complex, a widely utilized catalyst complex in asymmetric catalysis.

Development and tandem EPR study of an asymmetric Cu(II)-catalyzed spiroannulation

253rd National Meeting (2017)

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