Imidazole ring monoxide

The ring carbons of the imidazole ring presumably arise from carbon monoxide. Conceivably rhodium oxide is converted into HRh(CO)), which functions as a carbonylation reagent the oxide also functions as a reduction catalyst. 

Neutron diffraction studies have shown that the outermost oxygen atom of the boxmd O2 is hydrogen bonded to the H atom on the atom of the distal imidazole ring of His E7 (Fig. 16-10). Carbon monoxide binds with the C=0 axis perpendicular to the heme plane and unable to form a corresponding hydrogen bond. This decreases the affinity for CO and helps to protect us from carbon monoxide poisoning. 

The carbonylation of indolines at the 7-position with ethylene and carbon monoxide has been achieved when a 2-pyridyl group is substituted at the indoline nitrogen atom (eq 6). Fused imidazole rings in 1,2-disubstitutedbenzimdazoles also serve as the directing group to selectively undergo direct carbonylation at the 4-position (eq7).i2... 

Pyridine itself can be reacted with olefins and carbon monoxide in the presence of a catalytic amount of Ru3(CO)i2 to give a-acylated pyridines (eq 8)T A number of olefins react with the pyridine to afford the corresponding linear p)ridyl ketones as the major products. The ruthenium-catalyzed carbonylation of 1,2-disubstituted imidazoles with olefins and carbon monoxide provides C-C bond formation at the 4-position (eq Various functional groups, e.g., ether, acetal, ester, imide, and nitrile are tolerant to the reaction conditions. The reaction of 1-methylpyrazole under similar carbonylation conditions gives 3-pyrazolyl ketones (eq 10). This result is in contrast to the Friedel-Crafts acylation of a pyrazole ring, which yields 4-pyrazolyl ketones. ... 

---