在乙酸中用三(2,4-戊二酮基)锰(III)氧化萘以良好至中等产率得到二乙酰甲基衍生物。使用过量的氧化剂,乙酰甲基取代的萘被进一步氧化,得到 3-乙酰氧基-3-萘基-2,4-戊二酮。蒽的类似氧化也产生(二乙酰甲基)蒽以及进一步氧化的二乙酰亚甲基衍生物。发现当芳香族化合物的电离电位低于 8.12 eV 时,这种直接二乙酰甲基化是有效的,并且由三(2,4-戊二酮)锰(III)热解直接产生的二乙酰甲基自由基具有基于取代萘氧化的结果的亲电性。
Manganese(III)-mediated carbon-carbon bond formation in the reaction of xanthenes with active methylene compounds
摘要:
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.