Catalytic Synthesis and Asymmetric Reduction of Pyridylglyoxylic Amides and Esters
Résumé
The preparation of 2‐pyridyl‐ and 4‐pyridylglyoxylic esters and amides in moderate to high yields via palladium‐catalyzed double carbonylation of 2‐iodo‐ and 4‐iodopyridines is reported. The effect of temperature, CO pressure, solvent, nature and concentration of nucleophile, nature of catalyst precursor, and substituents on iodopyridines has been investigated. The reduction of 4‐pyridylglyoxylate esters into the corresponding α‐hydroxy esters via ruthenium‐catalyzed asymmetric hydrogenation or using alpine‐borane proceeded in high yields but poor enantioselectivity. The results for the carbonylation and the hydrogenation catalytic processes are discussed in terms of electronic effects induced by the pyridyl ring.