Pyridazines. II. Intramolecular Cycloaddition of 3-Substituted-6-[2-(2-methylallyl) phenoxy] pyridazines

Heating of 3-phenyl-, 3-methyl, and 3-chloro-6-[2-(2-methylallyl) phenoxy] pyridazine in diethylaniline or without a solvent afforded 2-substituted-9a-methyl-1, 9a-dihydroxanthenes, which are previously unknown group of compounds. The mechanism of this reaction may be explained by an intramolecular cycloaddition between pyridazine nucleus and the allylic side chain to give the (4+2)π adduct followed by N2 elimination. Similarly, cyclization of 1-phenyl-4-[2-(1-methylallyl)-1-naphthyloxy] phthalazine gave 5-phenyl-6a-methyl-6a, 12a-dihydro-7H-benzo [c] xanthene.