[reaction: see text] Thermal decomposition of phenyliodonium ylide of 2-hydroxy-1,4-naphthoquinone (lawsone) in the presence of indole derivatives affords 3-acylated indoles existing in their enol forms, through a ring contraction and alpha,alpha'-dioxoketene formation reaction. The same reactants afford 3-(3-indolyl)-2-hydroxy-1,4-naphthoquinones in a copper-catalyzed reaction. Enamines, among other C-nucleophiles tested, give analogous results.

Aryliodonium ylides of 2-hydroxy-1,4-naphthoquinone react with amines in refluxing dichloromethane to afford good yields of indanedione 2-carboxamides 5, through a ring-contraction and alpha,alpha'-dioxoketene formation reaction. These amides exist in solution in an unusual enol-amide form. In contrast, the same reactants in a copper-catalyzed reaction afford arylamines and 3-iodo-4-hydroxy-1,2-naphthoquinone.

The highly reactive indanedioneketene 5, resulting from the thermal decomposition of phenyliodonium ylide of 2-hydroxy-1,4-naphthoquinone (lawsone, 4), in the absence of nucleophiles dimerizes to the corresponding tetraoxo spiro oxetanone 6 in quantitative yield. This oxetanone exhibits an interesting reactivity toward amines.

Indenocarboxamides, resulting from the sequential addition of two arylamine equivalents to indanedione ketene dimer, are oxidized by [bis(trifluoroacetoxy)iodobenzene] to fused indeno-1,4-diazepinones in yields depending on the substituents on both aromatic rings. A plausible reaction pathway explaining the formation of the title compounds, as well as the formation of the two other minor products of the reaction, through a common intermediate, is suggested.

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