Reaction of Anthranils with Enamines Novel Synthesis of Quinolines

Abstract

It was found that the quinoline derivatives are formed by the reaction of benz[ c ]isoxazoles (anthranils) with enamines. For example, 2, 3-dihydro-1 H-cyclopenta[ b ]quinoline was obtained by the reaction of anthranil with 4-(1-cyclopentenyl)morpholine (70% yield). The reaction may proceed via a quinoline N-oxide, which was formed from the [4+2]cycloadduct of anthranil with the enamine. In fact, quinoline N-oxides were occasionally isolated.
In the presence of a low valence titanium salt (prepared from titanium(IV) chloride and zinc dust), the reaction proceeded smoothly under mild conditions, and 1, 2, 3, 4-tetrahydroacridine was easily synthesized from anthranil and 1-(1-cyclohexenyl)pyrrolidine (yield : 78%).