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M. Rueping, E. Sugiono
Scheme 1. Synthesis of differently substituted BINOL-phosphosphates 5 and 6
dropyridine 2a yields the chiral amine 7 and pyridinium salt B, which
undergoes proton transfer to regenerate the Brønsted acid catalyst 5
(Fig. 3).
Fig. 3. Proposed mechanism for the transfer hydrogenation