Pyridazines. LXXXIV. Studies on borohydride reduction of pyridazine compounds

Imidazo1,2-b]pyridazine, s-triazolo4,3-b]pyridazine and tetrazolo1,5-b]pyridazine and some derivatives thereof were reduced with sodium borohydride to give the corresponding 5,6,7,8-tetrahydro derivatives. A mechanism for these reductions is proposed and reduction at the C₇-C₈ bond occurs before the reduction of the C₆? N₅ bond. Substituents at position 7 and/or 8 cause a significant decrease in the extent of reduction or lead to a 5,6-dihydro derivative by competitive attack at the 6 position.