The role of lithium amides as reducing agents in a novel pathway to 3,6-diarylpyridazines by ring transformations of 3,6-diaryl-s-tetrazines

Abstract

3,6-Diaryl-s-tetrazines undergo two competing reactions when treated with lithium amides. The first, direct nucleophilic attack and addition of lithium amide to the tetrazine, appears to be predominant when a less hindered amide is used, and moderate quantities of tetrazine are then regenerated on quenching. The competing reaction, which is seen more clearly with a bulkier amide such as lithium di-isopropyl-amide, involves reduction of tetrazine to a dihydro derivative with concomitant formation of imine from the amide: this imine is then attacked by further amide and gives rise to a charged intermediate which reacts with more tetrazine to form a pyridazine.