ORGN 562 |
| Catalyzed exchange of hydrogens for deuterium or tritium has become an increasingly important approach to the preparation of isotopically labeled compounds as a result of the development of new, efficient and regioselective catalytic systems. Among these, organoiridium complexes, such as [(cod)Ir(PPh3)2]BF4 and [(cod)Ir(PCy3)(py)]PF6, are frequently used for labeling of aryl derivatives possessing an appropriate iridium-coordinating function, which directs C-H activation to the ortho sites. Substrates possessing meta-substituents have nonequivalent ortho C-H bonds; however, little information is available about the influence meta-substituents have upon their selectivity. We have monitored the progress of organoiridium-catalyzed deuteration at the C2 and C6 positions in C3-substituted acetophenones and N,N-dimethylbenzamides by 1H NMR. There are marked differences in the rates of deuteration at the two sites. Non-coordinating C3-substituents retard C2 labeling relative to C6; however, coordinating substituents can counteract this effect, in some cases to the extent that C2-deuteration is favored over that at C6.
|
|
Physical Organic Chemistry, Metal-Mediated Reactions, Asymmetric Reactions and Syntheses
8:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Organic Chemistry |
