SYNTHESIS OF NEW NITROGEN-BRIDGED HETEROCYCLES - REACTION OF PYRIDINIUM N-IMINES WITH CYCLOPROPENONES

Pyridinium N-imine salts 3 and 5-8 reacted smoothly with methylphenylcyclopropenone (2) in methylene chloride in the presence of triethylamine at room temperature to give the corresponding 2-methyl-4-phenyl-3ff-pyrido[l,2-6]pyridazin-3-ones 14-19 in fairly good yields. 4,4a-Dihydro intermediates 10-13 were isolated from the reactions of 3, 4, and 9. Reaction of 2 with 3 in methanol containing triethylamine afforded d-amino ester 22 in addition to 14. Dipropylcyclopropenone (24) did not react with pyridinium N-imine salts in methanol containing triethylamine at room temperature, but did furnish 2,4-dipropyl-3H-pyrido[ 1,2-6 ]pyridazin-3-ones 25-28 with 3 and 5-7 under reflux conditions. Possible mechanisms of this reaction are discussed. © 1978, American Chemical Society. All rights reserved.