Spiro-Bicyclic Bisborane Catalysts for Metal-Free Chemoselective and Enantioselective Hydrogenation of Quinolines.

A new series of spiro-bicyclic bisborane catalysts has been prepared by means of hydroboration reactions of C2 -symmetric spiro-bicyclic dienes with HB(C6 F5 )2 and HB(p-C6 F4 H)2 . When used for hydrogenation of quinolines, these catalysts give excellent yields and enantiomeric excesses, and show turnover numbers of up to 460. The most attractive feature of these metal-free hydrogenation reactions was the broad functional-group tolerance, making this method complementary to existing methods for quinoline hydrogenation.