Catalytic Synthesis and Asymmetric Reduction of Pyridylglyoxylic Amides and Esters

Abstract

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.