Synthesis of Novel 6-(2-Thienyl)-2,2′-Bipyridine Ligands Using “1,2,4-Triazine” Methodology: an Unexpected Demethylation During the Aza-Diels-Alder Reaction with 2,5-Norbornadiene

Abstract

New 2-(di)methoxythienyl substituted ligands of the 2,2′-bipyridine series containing various aromatic substituents at the C3 position were obtained in yields of up to 90 %. A “1,2,4-triazine” methodology involving an S<inf>N</inf>H reaction in 1,2,4-triazine followed by an aza-Diels-Alder reaction with 2,5-norbornadiene was used to synthesize the target compounds. When the Diels-Alder reaction was carried out in an autoclave, an unexpected demethylation reaction was observed, leading to the formation of oxo-thienyl substituted products. A mechanism for the reaction that occurred has been proposed on the basis of identified byproducts. Preliminary studies on the photophysical and coordination properties of the obtained compounds were also carried out. In particular, the possibility of obtaining a platinum(II) complex with the demethylation product was demonstrated. © 2024 Wiley-VCH GmbH.