Manganese(III)-mediated carbon-carbon bond formation in the reaction of xanthenes with active methylene compounds
作者:Hiroshi Nishino、Hironori Kamachi、Harumi Baba、Kazu Kurosawa
DOI:10.1021/jo00039a010
日期:1992.6
Oxidation of xanthenes with manganese(III) acetate in the presence of active methylene compounds such as 1,3-dicarbonyl compounds, malononitrile derivatives, acetone, and nitromethane selectively gives 9-substituted xanthene derivatives in good yields. A similar oxidation of thioxanthene also yields 2-(9-thioxanthenyl)-1,3-dicarbonyl compounds in 57-91% yields. The obtained 2-(9-xanthenyl)-1,3-dicarbonyl compounds are readily converted to 2-(9-xanthenylidene)-1,3-dicarbonyl derivatives using manganese(III) complexes or 2,3-dichloro-5, 6-dicyano-1,4-benzoquinone. The mechanisms for the formation of 9-substituted xanthenes are discussed on the basis of the reaction of intermediates, the electron-donating substituent effect on the xanthene ring system, effect of additives, and comparison with a reaction of radical-trapping reagents.