Solvent vs. counterion acceleration of enantioselective carbo and hetero Diels–Alder reactions

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Mogens Johannsen and Karl Anker Jørgensen


Abstract

The influence of solvents (CH2Cl2 and CH3NO2) vs. non-coordinating counterions (OTf and SbF6; Tf = CF3SO2) on the catalytic properties of CuX2–bisdihydrooxazoles in carbo and hetero Diels–Alder reactions has been studied. It has been observed that the use of CH3NO2 as the solvent enhances the reactivity of the Cu(OTf[hair space])2–bisdihydrooxazole catalyst compared with the reactivity of CuX2–bisdihydrooxazole in CH2Cl2 in these reactions. The use of CH3NO2 as the solvent in the carbo Diels–Alder reaction gives an 87% yield of the Diels–Alder adduct with 96% enantiomeric excess (ee), while in the hetero Diels–Alder reaction 98% yield and 97% ee is found under similar reaction conditions.


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