Divergent Conversion of 4-Naphthoquinone-substituted 4<i>H</i>-Isoxazolones to Different Benzo-fused Indole Derivatives
Michael S. Christodoulou, Sabrina Giofrè, Egle M. Beccalli, Francesca Foschi, Gianluigi Broggini
Abstract
4,4-Disubstituted 4H-isoxazol-5-ones bearing a 1,4-naphthoquinone moiety undergo transformation into different types of benzoindolyl products depending on the different reaction conditions. A decarboxylative ring opening/ring closure promoted by catalytic [Ru(p-cymene)2Cl2]2 yields benzo[f]indole-4,9-diones. Alternatively, hydrogenation reactions provide the conversion of 4-(1,4-naphthoquinone)-substituted isoxazol-5-ones to benzo[g]indole compounds, with the level of reduction depending on the substituents present on the ring. Starting materials have been easily prepared by the functionalization of isoxazolinones with naphthoquinone under mild conditions.