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M. Rueping, E. Sugiono
Fig. 6. Proposed mechanism of the Brønsted acid catalyzed transfer hydrogenation of quinolines
substituted tetrahydroquinolines with excellent enantioselectivities and
good isolated yields. The mild reaction conditions of this metal-free
process, the operational simplicity and practicability, as well as the low
catalyst loading render this transformation an attractive approach to optically active tetrahydroquinolines and their derivatives. This we have
demonstrated in the enantioselective synthesis of the naturally occurring alkaloids Galipinine, Cuspareine and Angustureine.