Truly Catalytic and Enantioselective Pinacol Coupling of Aryl Aldehydes Mediated by Chiral Ti(III) Complexes<sup>†</sup>
作者:A. Chatterjee、T. H. Bennur、N. N. Joshi
DOI:10.1021/jo0342875
日期:2003.7.1
A variety of chiral Ti(IV) complexes were reduced in situ with zinc in acetonitrile. The resulting chiral Ti(III) complexes were found to catalyze the pinacol coupling reaction stereoselectively. The best results were obtained from the Ti-SALEN complex, which was found to be an efficient catalyst at 10 mol % concentration. Various aromatic aldehydes were coupled to obtain chiral hydrobenzoin derivatives
Hydrogen Bonding-Assisted Enhancement of the Reaction Rate and Selectivity in the Kinetic Resolution of <i>d,l</i>
-1,2-Diols with Chiral Nucleophilic Catalysts
作者:Kazuki Fujii、Koichi Mitsudo、Hiroki Mandai、Seiji Suga
DOI:10.1002/adsc.201700057
日期:2017.8.17
An extremely efficient acylative kineticresolution of d,l‐1,2‐diols in the presence of only 0.5 mol% of binaphthyl‐based chiral N,N‐4‐dimethylaminopyridine was developed (selectivityfactor of up to 180). Several key experiments revealed that hydrogen bonding between the tert‐alcohol unit(s) of the catalyst and the 1,2‐diol unit of the substrate is critical for accelerating the rate of monoacylation
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
Mechanochemistry‐Amended Barbier Reaction as an Expedient Alternative to Grignard Synthesis**
作者:Jagadeesh Varma Nallaparaju、Tatsiana Nikonovich、Tatsiana Jarg、Danylo Merzhyievskyi、Riina Aav、Dzmitry G. Kananovich
DOI:10.1002/anie.202305775
日期:2023.9.25
Use of mechanochemistry enabled the rapid in situ generation of Grignard reagents, thereby overcoming the longstanding limitations of the Magnesium-mediated Barbier reaction in solution.
机械化学的使用使得格氏试剂能够快速原位生成,从而克服了溶液中镁介导的巴比尔反应的长期限制。
Synthesis and Stereochemical Characterization of Some Optically Active 1,2-Dinaphthylethane-1,2-Diols
Three new diols, 1,2-di(2-naphthyl)ethane-1,2-diol, 1-(1-naphthyl)-2-(2-naphthyl)ethane-1,2-diol, and 1,2-di(1-naphthyl)ethane-1,2-diol, have been prepared in optically active form by catalytic asymmetric syn-dihydroxylation of the corresponding (E)-olefins. The complete stereochemical characterization was easily accomplished by transforming them into the corresponding isopropylidene ketals. These derivatives can be separated by HPLC on a Chiralcel OD column allowing the determination of the ee, and at same time, their CD spectra have been analyzed, allowing a safe assignment of absolute configuration in conjunction with molecular mechanics calculations and an exciton-coupling treatment.