synthesizing the target molecules. The perfect chemoselectivity between aromatic and aliphatic aldehydes is difficult to achieve by the previous methods. The aromatic aldehyde-selective nucleophilic addition in the presence of aliphatic aldehydes was newly accomplished. Namely, the aromatic aldehyde-selective nucleophilic addition using arenes and allyl silanes proceeded in the presence of trialkylsilyl
condition using cetyltrimithylammonium bromide (CTAB) as surfactant. This solid was characterized using several techniques e.g. powder X-ray diffraction (XRD), N2 adsorption-desorption, FT-IR, TG/DTG and pyridine adsorption-desorption followed by IR spectroscopy. The catalytic performance of Al-MCM-41 catalyst as Lewis acid was used without treatment and was compared with TiCl4 in the allylation of aromatic
摘要 以十六烷基三甲基溴化铵(CTAB)为表面活性剂,在水热条件下合成了Si/Al比为12.5的介孔Al-MCM-41分子筛。使用几种技术表征该固体,例如粉末 X 射线衍射 (XRD)、N2 吸附-解吸、FT-IR、TG/DTG 和吡啶吸附-解吸,然后是红外光谱。Al-MCM-41 催化剂作为路易斯酸的催化性能在未经处理的情况下使用,并与 TiCl4 在芳族醛与烯丙基三甲基硅烷的烯丙基化反应中进行了比较。结果表明,在 Al-MCM-41 的存在下,无论芳香醛的性质如何,在 35 °C 的温度下都获得高烯丙基甲硅烷基醚。当使用 TiCl4 时,反应需要 -85 °C 的温度,并且获得的所有产物都是由于二烯丙基化。为了解释在 Al-MCM-41 或 TiCl4 存在下这种不同的烯丙基化,提出了两种可能的反应机制。Al-MCM-41 用于连续四次实验,没有明显的活性损失,证实了它的稳定性。最后,
Enhancement of Lewis Acidity
by Ligand-Defined Metal Geometry: A Catalytic Allylation
of Aldehydes with Allyltrimethylsilane
A highly Lewis acidic aluminum complex was produced using a tridentate ligand 1. The enhancedLewisacidity of 1-Al was attributed to the combination of a stereoelectronic effect and an electrostatic effect. Comparison with an unstrained complex 4-Al indicated that the ligand-defined sp 3 geometry of the aluminum in 1-Al led to the lower LUMO level and the larger LUMO coefficient on the aluminum. 1-Al
Chlorotrimethylsilane combined with acetonitrile has characteristically promoted allylation of carbonyl compounds by diallyldibutyltin to produce a variety of homoallyl silyl ether in good yields, while the addition of HMPA or LiCl disturbed the allylation.
A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the reaction of both carbonyl compounds and acetals with allylsilanes to afford the corresponding homoallyl silyl ethers and homoallyl alkyl ethers, respectively. Both the mesoporous structure and the presence of aluminum moiety were indispensable for the high catalytic activity of Al-MCM-41. Moreover, Al-MCM-41 could catalyze the reaction of acetals chemoselectively in the presence of the corresponding carbonyl compounds. The solid acid catalyst Al-MCM-41 could be recovered easily by filtration and could be reused three times without a significant loss of catalytic activity. (C) 2011 Elsevier Ltd. All rights reserved.