Microwave-Assisted Synthesis of 3,6-Di(pyridin-2-yl)pyridazines: Unexpected Ketone and Aldehyde Cycloadditions

3,6-Di(pyridin-2-yl)pyridazines are an interesting class of compds. because of their metal-coordinating ability resulting in the self-assembly into [2*2] gridlike metal complexes with copper(I) or silver(I) ions. These and other substituted pyridazines can be prepd. by the inverse-electron-demand Diels-Alder reactions between acetylenes and 1,2,4,5-tetrazines. In this contribution, the effect of (superheated) microwave conditions on these generally slow cycloaddns. is described. The cycloaddn. of acetylenes to 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine could be accelerated from several days reflux in toluene or N,N-dimethylformamide to several hours in dichloromethane at 150 DegC. In addn., the unexpected cycloaddn. of the enol tautomers of various ketones and aldehydes to 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine is described in detail providing an alternative route for the synthesis of (substituted) pyridazines. [on SciFinder (R)]