Radical-mediated cyclisation of ω-aryl-β-dicarbonyl compounds to tetrahydrobenzocyclohepten-6-ones, hexahydrobenzocycloocten-6-ones and naphthalen-2(1H)-ones

Abstract

Manganese(III) acetate in acetic acid promotes efficient radical-mediated oxidative cyclisation of ε-aryl-β-dicarbonyl and Z-γ,δ-unsaturated δ-aryl-β-dicarbonyl compounds carrying electron-releasing groups in the aromatic ring, forming 6,7,8,9-tetrahydro-5H-benzocyclohepten-6-ones and naphthalen-2(1H)-ones, respectively. The process is accompanied by secondary acetoxylation at the activated benzylic position of the initial cyclisation products, and is exemplified by the conversions of the ε- and δ-aryl-β-dicarbonyl compounds 6 and 11 into the benzocycloheptenone 18 and the naphthalenone 21, respectively. Application of the oxidation to the formation of 8-membered hexahydro- and tetrahydro-benzocycloocten-6-ones 19 and 22 from ζ-aryl-β-dicarbonyl and Z-γ,δ-unsaturated ζ-aryl-β-dicarbonyl compounds is limited by low reactivity, and in the latter case, by radical rearrangement followed by cyclisation to a tetralin.