Research Center for Solar Energy Chemistry and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan.
J Org Chem. 2010 Mar 5;75(5):1450-7. doi: 10.1021/jo902321f.
We previously found that photoirradiation of an acetone/water mixture containing olefins affords the corresponding methyl ketones highly efficiently and selectively via a water-assisted C-C coupling between the acetonyl radical and olefins (Org. Lett. 2008, 10, 3117-3120). The reaction proceeds at room temperature without any additives and has a potential to be a powerful method for methyl ketone synthesis. Here we report that an addition of Mg(2+)-exchanged zeolite Y (MgY) to the above photoreaction system accelerates the methyl ketone formation, while maintaining high selectivity. Ab initio molecular orbital calculation reveals that the accelerated methyl ketone formation is due to the electrostatic interaction between Mg(2+) and excited-state acetone. This leads to a charge polarization of the carbonyl moiety of excited-state acetone and accelerates the hydrogen abstraction from ground-state acetone (acetonyl radical formation). This promotes efficient addition of the acetonyl radical to olefins, resulting in methyl ketone formation enhancement. Adsorption experiments reveal that accumulation of olefins inside the zeolite pore also affects efficient radical addition to olefins. The present process successfully produces various methyl ketones with very high yield, and the MgY recovered can be reused for further reaction without loss of activity.
我们之前发现,在含有烯烃的丙酮/水混合物中进行光照射,可以通过丙酮基自由基与烯烃之间的水辅助 C-C 偶联,高效且选择性地得到相应的甲基酮(Org. Lett. 2008, 10, 3117-3120)。该反应在室温下进行,无需任何添加剂,具有成为一种强大的甲基酮合成方法的潜力。在这里,我们报告说,将 Mg(2+)-交换沸石 Y(MgY)添加到上述光反应体系中,可以加速甲基酮的形成,同时保持高选择性。从头算分子轨道计算表明,加速的甲基酮形成是由于 Mg(2+)与激发态丙酮之间的静电相互作用。这导致激发态丙酮的羰基部分发生电荷极化,并加速从基态丙酮中提取氢(形成丙酮基自由基)。这促进了丙酮基自由基对烯烃的有效加成,导致甲基酮形成的增强。吸附实验表明,烯烃在沸石孔内的积累也会影响自由基对烯烃的有效加成。该过程成功地以很高的产率生产了各种甲基酮,并且回收的 MgY 可以在没有活性损失的情况下重复用于进一步的反应。