Titanium-catalyzed asymmetric epoxidation of non-activated olefins with hydrogen peroxide.
Titanium-catalyzed asymmetric epoxidation of non-activated olefins with hydrogen peroxide.
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DOI：
10.1002/anie.200700949
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发表时间：
2007-06
影响因子：
--
通讯作者：
Y. Sawada;Kazuhiro Matsumoto;T. Katsuki*
中科院分区：
文献类型：
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作者：
Y. Sawada;Kazuhiro Matsumoto;T. Katsuki*
烯烃不对称环氧化是合成高效中间体--富对映体环氧化物的有效方法。因此，在过去的几十年里，人们对催化不对称环氧化反应进行了广泛的研究，报道了一些以钛、[2]锰、[3]钒、[5]钼为基础的优良过渡金属催化剂，以及手性酮等有机催化剂。然而，这些反应需要原子效率较低的氧化剂，如大体积的烷基过氧化氢和氧。从绿色可持续发展的观点来看，开发低成本、高原子效率、易于操作和生态无害(不产生危险废物)的过氧化氢不对称环氧化反应已成为工业界和学术界的强烈愿望。[7]最近，我们发现，二μ-氧代钛(Salalen)和二μ-氧代钛(Salalen)络合物是催化双氧水不对称环氧化烯烃的有效催化剂。[8]在室温下，二μ-氧代钛(Salalen)络合物1(图1)对共轭烯烃的环氧化反应具有很高的转化率(最高可达4600)和很高的对映体选择性。我们还初步考察了1-辛烯的环氧化反应，得到了82%的对映体选择性。脂肪族烯烃(非活性烯烃)与双氧水的不对称环氧化反应的发展是一个高度优先的问题；然而，用于该反应的催化剂很少。虽然Strukul和他的同事报道了一种铂催化剂，但它只应用于没有α支链的末端烯烃。[9]在这里，我们描述了非活性烯烃与过氧化氢的不对称环氧化反应，该反应是通过钛(Salalen)络合物1实现的，底物范围要宽得多。
Asymmetric epoxidation of olefins is a potent method for synthesizing enantioenriched epoxides that are high-utility intermediates. Thus, over the past few decades, extensive research efforts have been devoted to the development of catalytic asymmetric epoxidation,[1] and some excellent transition-metal catalysts based on titanium,[2] manganese,[3] vanadium,[4] and molybdenum [5] as well as organocatalysts such as chiral ketones [6] have been reported. However, these reactions require oxidants of lower atom-efficiency such as bulky alkyl hydroperoxides and oxones. From the viewpoint of green sustainability, the development of asymmetric epoxidation using aqueous hydrogen peroxide that is lowcost, highly atom-efficient, easy-to-handle, and ecologically benign (no production of hazardous waste), has been strongly desired in industry and academic research.[7] Recently, we found that di-μ-oxo titanium (salalen) and diμ-oxo titanium (salan) complexes serve as efficient catalysts for asymmetric epoxidation of olefins using aqueous hydrogen peroxide.[8] The epoxidation of conjugated olefins with the di-μ-oxo titanium (salalen) complex 1 (Figure 1) proceeded with high turnover numbers (up to 4600) as well as high to excellent enantioselectivity at room temperature. We also preliminarily examined epoxidation of 1-octene and obtained a high enantioselectivity of 82% ee.The development of asymmetric epoxidation of aliphatic olefins (non-activated olefins) with aqueous hydrogen peroxide is a high-priority issue; however, there are just a few catalysts for the reaction. Although a platinum catalyst was reported by Strukul and co-workers, it has been applied only to terminal olefins with no α branches.[9] Herein, we describe asymmetric epoxidation of non-activated olefins with aqueous hydrogen peroxide, which was achieved by using titanium (salalen) complex 1 and had a much wider substrate scope.