Syntheses and pKa Determination of 1-(o-Hydroxyphenyl)imidazole Carboxylic Esters.

All three isomers of 1-(o-hydroxyphenyl)imidazole carboxylic esters (1–3) have been synthesized regioselectively via their methyl ether precursors. Methyl 1-(o-methoxyphenyl)imidazole-2-carboxylate (6) and the corresponding 1,4-isomer (11) were synthesized via Cu-catalyzed coupling of 2-iodoanisole with imidazole followed by methoxycarbonylation, and by direct coupling of 2-iodoanisole with methyl imidazole-4-carboxylate (7), respectively. The 1,5-isomer (15) was prepared by annulation of an N-aryl glycine ester derivative (13). The boron tribromide mediated cleavage of methyl ethers gave the hydroxyphenyl compounds (1–3) in good to excellent yields. These compounds can serve as building blocks for synthesizing a new generation of active-site model compounds of cytochrome c oxidase (CcO). The pKa values have been determined by spectrophotometric measurements in order to provide a basis for the understanding of the proton transfer processes in CcO.