Ferrocene derivatives. Part 25. Their use in the synthesis of 5H-cyclopenta[c]quinolines and 5,6-dihydro-5-azabenz[e]azulenes

Abstract

Arylation of ferrocene with o-nitro- and o-cyano-benzenediazonium salts leads smoothly to the o-nitro- and o-cyano-phenylferrocenes. These are reduced to o-ferrocenylaniline and o-ferrocenylbenzylamine respectively. Bischler–Napieralski cyclisation of the N-acyl derivatives of these amines proceeds with (partial) loss of iron to give the title compounds. The intermediate ferrocene-heterocycles, if isolated may be cleaved to the same products by exposure to diffuse daylight in aqueous acid solution. The liberation of 2,3,4.5-tetrahydrocyclopent[c]azepines by photolysis of the corresponding cyclopentadienyliron complexes in acidic medium is also briefly examined.