SYNTHESIS OF NOVEL RIGID NORBORNYLOGOUS SPACERS BEARING HETEROCYCLIC LIGANDS FOR THE INVESTIGATION OF LONG-RANGE INTRAMOLECULAR ELECTRON-TRANSFER INVOLVING METAL CENTERS

The synthesis of some novel 1,4-dimethoxynaphthalene-bridge-heterocycle systems is described. In these systems, the naphthalene and heterocyclic groups are fused to a rigid bridge consisting of linearly fused norbornyl and bicyclo[2.2.0]hexyl groups, Bridges used herein have relays of 2-, 4-, and 6-bonds long. The heterocycle is either 3,6-di(2-pyridyl)-pyridazino, or pyrido and was attached to the bridge by annulation methods. The pyridazino systems, 2(m,n), were synthesized via Diels-Alder reaction of 3,6-di(2-pyridyl)-1,2,4,5-tetrazine with the alkenes, 13 and 6(m,n), and subsequent aromatization of the adducts with DDQ. Pyridine annulation was successfully carried out using two different methods: (i) Boger pyridine annulation of ketones, 11, 20b, and 21b, (with 1,2,4-triazine and pyrrolidine); (ii) Diets Alder reaction of alkenes 13 and 6(m,n) with 3-thiomethyl-1,2,4-triazine, followed by Raney nickel reductive desulfurization of the aromatized adducts. The synthesis of Ru(II)(2,2'-bipyridyl)2 complexes of the pyridazino systems, 9(m,n) and 10, is also described.