Asymmetric Hydrogenation of Quinoxalines, Benzoxazines, and a Benzothiazine Catalyzed by Chiral Ruthenabicyclic Complexes

The ruthenabicyclic complex RuCl[(R)‐daipena][(R)‐dm‐segphos] with potassium tert‐butoxide catalyzes the hydrogenation of 2‐alkylquinoxalines and a 3‐methyl‐2H‐1,4‐benzoxazine in toluene under 20–100 atm of hydrogen at 40 °C to afford S‐configured cyclic amino products in greater than 97% enantiomeric excess {DAIPENA=anion of DAIPEN at the 2‐position of an anisyl group, DAIPEN=1,1‐di(4‐anisyl)‐2‐isopropyl‐1,2‐ethylenediamine, DM‐SEGPHOS=(4,4′‐bi‐1,3‐benzodioxole)‐5,5′‐diylbis[di(3,5‐xylyl)phosphine]}. The high catalytic activity results in a turnover number as high as 9400. Hydrogenation of the benzoimine heterocycles with the RuCl[(R)‐daipena][(R)‐segphos]/potassium tert‐butoxide system yields the R‐configured products in high enantiomeric excess [SEGPHOS=(4,4′‐bi‐1,3‐benzodioxole)‐5,5′‐diylbis(diphenylphosphine)]. The mode of enantioselection is discussed based on transition state models involving six‐membered pericyclic structures. magnified image