Exploring the structural space of a chiral pyroborate catalyst for the asymmetric transfer hydrogenation of quinolines

ORGN 708

Aman A. Desai, desaiaman@chemistry.msu.edu and William D. Wulff, wulff@chemistry.msu.edu. Department of Chemistry, Michigan State University, 529 Chemistry, East Lansing, MI 48824
Chiral borate catalysts derived from vaulted biaryl ligands and triphenylborate have been extensively utilized in our laboratories for the discovery and development of several highly efficient asymmetric reactions. Structural studies resulted in the tentative assignment of a pyroborate as the active catalyst. Recent studies have revealed that this in-situ generated catalyst can also be formed by using BH3.SMe2, water and phenol instead of triphenylborate, affording the same level of catalyst activity. This discovery lent us the distinct opportunity to explore the structural space of this novel chiral pyroborate catalyst, by using alcohols of varying electronic and steric properties. The asymmetric transfer hydrogenation of quinolines was chosen as a model reaction, and 36 different alcohols were tested. The results were gratifying in that the entire gamut of asymmetric induction was observed (-12 to 78% ee), thus establishing the importance of this region in the structural space of the pyroborate catalyst.