Abstract
Palladium-catalyzed asymmetric Heck reactions have been performed
using high temperature conditions with the aid of controlled microwave
dielectric heating. Significant enantioselectivities of up to 92% ee
were obtained under non-inert conditions utilizing the previously
reported thermostable palladium-phosphineoxazoline catalytic
system. With microwave irradiation, reaction times of hours instead
of days were obtained. Enantiomeric purities and conversions were
found to be strongly dependent on both the choice of the aryl triflate,
the reaction temperature, the solvent and the base. Examples of
asymmetric arylations of electron-rich as well as neutral cyclic
alkenes are presented.
Key words
asymmetric catalysis - Heck reaction - arylations - regioselectivity - palladium
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