离子液体,即[甜菜碱][H 2 PO 4 ],被发现是无溶剂条件下xanthen-9-ol与不同亲核试剂直接取代反应的有效催化剂。该催化体系易于操作,后续后处理程序简单,离子液体催化剂可在高催化活性水平下重复使用至少五个循环。此外,离子液体制备简单,原料廉价,生物相容性好。因此,我们的研究提出了一种有趣且可持续的直接替代酒精的方案。
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.
Reaction of Thiaxanthydrol With Compounds Containing Active Hydrogen<sup>1</sup>