Facile synthesis of polypyridine esters: A route to functionalized aldehydes

A wide range of ester-substituted oligopyridines, based on pyridine, 1,8-na phthyridine, 1,10-phenanthroline, 2,2'-bipyridine, and 2,2':6',6 " -terpyri dine units, has been synthesized and fully characterized. The principal rea ction involves the palladium(0)-catalyzed carboalkoxylation of the bromo-, chloro- or triflate-substituted pyridine unit with carbon monoxide in the p resence of a primary alcohol as nucleophile and a tertiary amine as base. M onofunctionalization of disubstituted compounds is realized by reaction in ethanol under mild conditions (70 degreesC, 1 atm CO). Stepwise reduction o f selected esters with sodium borohydride, followed by Swern oxidation, aff ords the corresponding carbaldehydes in good yield. Several products are re ported for the first time. The synthetic methods reported herein represent a valuable approach to the large-scale preparation of ester-functionalized oligopyridines that can be subsequently transformed to the corresponding al cohols or acids. These procedures also provide a practical methodology to t he rational design of ligands bearing different kinds of functionalities.