redox-active titanium complex. Taking advantage of the well-tailored photoredox potential of this organic dye, the selective reduction of Ti(IV) to Ti(III) is achieved. These conditions enable the formation of the D,L (syn) diastereoisomer as the favored product of the pinacol coupling (d.r. > 20 : 1 in most of the cases). Moreover, employing a simply prepared chiral SalenTi complex, the new photoredox
频哪醇偶联反应是羰基化合物的还原偶联反应,在电子供体存在下通过形成酮基自由基进行,一步即可得到相应的 1,2-二醇。这种转化的光氧化还原形式已经使用不同的有机染料或光活性金属配合物在牺牲供体(例如叔胺或 Hantzsch 酯)的存在下完成。通常,这种反应性酮基自由基的均偶联既不是非对映选择性也不是对映选择性。在此,我们报道了由 5 mol% 的无毒、廉价且可用的 Cp 2 TiCl 2促进的芳香醛的高度非对映选择性频哪醇偶联反应。复杂的。允许完全控制非对映选择性的关键特征是在氧化还原活性钛络合物存在下使用吸收红色的有机染料。利用这种有机染料精心设计的光氧化还原电位,实现了将 Ti( IV ) 选择性还原为 Ti( III )。这些条件能够形成D , L ( syn ) 非对映异构体作为频哪醇偶联的有利产物(在大多数情况下,dr > 20:1)。此外,使用简单制备的手性 SalenTi 配合
Synthesis of homochiral dibenzo[b,f]phosphepin 5-oxides using a double ortho-lithiation strategy
作者:Stuart Warren、Paul Wyatt
DOI:10.1016/0957-4166(96)00099-7
日期:1996.4
Enantiomerically pure chiral seven membered phosphorus heterocycles - phosphepins - have been prepared by McMurry coupling, Sharpless dihydroxylation, ortho-lithiation and reaction with PhPCl(2) or PrPCl2. Studies of the ortho-lithiation and of hydrolysis of phosphepinium salts are included. Copyright (C) 1996 Elsevier Science Ltd
Synthesis, X-ray structures and chemistry of enantiomerically pure 10,11-dihydro-5-phenyl-5H-dibenzo[b,f ]phosphepine 5-oxides
Several phosphepine oxides were synthesised in optically pure form. Sharpless asymmetric dihydroxylation was used to introduce the chiral centres in all cases. Ring closure was achieved using either PhPCl2 or PrPCl2 together with a double nucleophile generated by either a double ortho-lithiation or double bromineâlithium exchange. The X-ray crystal structures of three phosphepine oxides illustrate their different conformations. The NMR spectra of several phosphepine oxides are described as is the chemistry which is shown to differ from that of acyclic phosphine oxides.