Abstract
The cyclization of 4-diazo-3-[N-(2-propenyl)amido]cyclohexadienones to cycloprop[c]indol-5-ones under the influence of copper(I) and copper(II) compounds has been investigated. Catalysis is observed with copper(I) triflate, the carbon monoxide complexe of copper(I) triflate, and the carbon monoxide complexes of trifluoropentanedionato- and hexafluoropentanedionatocopper(I). The best results, essentially quantitative conversion, are achieved with a catalyst solution containing trifluoropentanedionatocopper(I) carbonyl and 1 equiv of n-butalymine. No significant enantioselectivity is observed with a chiral salicyliminatocopper(II), [(trifluoroacetyl)camphorato]copper(I) carbonyl, or a trifluoropentanedionatocopper(I) carbonyl solution containing (S)-α-naphthylethylamine. A mechanistic interpretation involving reductive dediazonization, exo-trig radical cyclization, and cyclopropane formation by the resulting intermediate is proposed
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