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