Preparation of the first isobenzofuran containing two ring nitrogens : a new diels-alder diene for the synthesis of molecular scaffolds containing one or more end-fused 3,6-di(2-pyridyl)pyridazine ligands

Preparation of a stable, crystalline isobenzofuran containing two ring-nitrogen atoms, 4,7-di(2-pyridyl)-5,6-diazaisobenzofuran (diaza-IBF) (12), is reported here for the first time. Diaza-IBF was prepared using the s-tetrazine-induced fragmentation of 1,4-di(2pyridyl)-5,8-epoxy-5,8-dihydrophthalazine (9), for which a synthesis is provided. Diaza-IBF was also prepared by flash vacuum pyrolysis (FVP) of the isomeric N-methyl-1,4-di(2-pyridyl)-5,8-epoxy-5,6,7,8-tetrahydrophthalazine-6,7-dicarboximides (18) and (19), formed in three steps from furan, N-methyl maleimide, and 3,6-di(2-pyridyl)-s-tetrazine. Diaza-IBF was employed in cycloaddition protocols with alkenes to form scaffold mono- or bis-3,6-di-(2pryidyl)-pyridazine ligands having novel molecular architectures.