Polyhalogenoaromatic compounds. Part 44. Reactions of enamines with polyhalogenopyridines and their N-oxides

Abstract

1-Dialkylaminocyclohexenes were readily C-arylated by pentafluoropyridine or 3,5-dichlorotrifluoropyridine but pentachloropyridine was much less reactive. The resulting (tetrahalogenopyridyl)enamines did not cyclise on heating except in the case of compound (10), which gave the heterocycle (16). 1-Dialkylaminocycloalkenes and other enamines were C-arylated by pentachloropyridine N-oxide. In the cases of the dialkylaminocyclo-hexenes and -heptenes the expected pyridylenamines were accompanied by 1-(tetrachloro-2-pyridyl)cyclo-pentene and -hexene, respectively. A mechanism for the ring-contraction leading to the pyridylcycloalkenes is proposed involving a novel elimination of an N-formyldialkylamine.