Frustrated Lewis Pair catalyzed cycloisomerization initiated by hydride abstraction

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Cycloisomerizations, cycloadditions and electrocyclizations are powerful tools for the synthesis of complex molecular frameworks bearing quaternary stereogenic centers. In particular, iminium ions are recognized as reactive intermediates to induce such reactions. While acyclic tertiary iminium ions are readily accessible e.g. though condensation, substantial synthetic effort is required for the synthesis of the corresponding cyclic derivatives. However, the formation of iminium ions has been observed in frustrated Lewis pair-catalyzed reactions, which breaks new ground for the efficient access to these reactive intermediates.This research project takes advantage of this so far unexploited synthetic potential for the catalytic C–C bond forming reaction in the synthesis of quinoline derivatives bearing quaternary stereocenters. This important molecule class is obtained by hydride abstraction-initiated electrocyclization of catalytically formed iminium ions. The flexible substitution pattern opens up for the efficient access to polycyclic alkaloid derivatives with quaternary stereocenters. Furthermore, not only tetrahydroquinolines but also dihydroquinolines are accessible by this new catalytic approach. Through the choice of the catalyst the reaction can be directed to the redoxneutral cycloisomerization or to the so far unprecedented dehydrogenative cycloisomerization accessing two pharmacologically important product classes from the same substrate.