High yield preparation of 4'-(4-bromophenyl)-2,2':6',2''-terpyridine by a condensation reaction. Determination of the stereochemistry of two complex by-products by a combination of molecular mechanics and NMR spectroscopy

An improved high yield synthesis of 4'-(4-bromophenyl)-2,2': 6',2 ''-terpyridine from 2-acetylpyridine (1) and 4-bromobenzaldehyde (2) has been developed, using a two-step aldol condensation. In this, the intermediate azachalcone 3 was isolated, then reacted with N-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide, prepared from 1, using ammonium acetate both as a base and as a ring closure agent. It could also be shown that one step aldol condensation of 1 and 2 gave low yields of the desired terpyridine due to facile formation of polycondensation products, Two of these, 8 and 10, could be isolated in moderate yields from condensation reactions. The structure and relative configuration of these compounds were determined by a comparison of observed experimental NMR parameters with theoretical values. calculated by molecular mechanics.