Enantioselective pinacol coupling reaction of aromatic aldehydes catalyzed by chiral vanadium complexes

The asymmetric pinacol coupling of aromatic aldehydes by chiral salan–vanadium complexes as effective catalysts is reported. Chiral 1,2-diols were obtained with high diastereoselectivities (up to 90/10) and moderate to high enantioselectivities (up to 82% ee). The possible mechanism of the pinacol coupling reaction is also discussed.     

First examples of gold nanoparticles catalyzed silane alcoholysis and silylative pinacol coupling of carbonyl compounds

In this Letter, we illustrate the first catalytic application of supported Au nanoparticles in silane alcoholysis. The reaction proceeds with low amount of catalysts, under solvent free conditions for liquid substrates, without additional ligands and in a very selective way for primary alcohols in the examined cases. Additionally, a gold catalyzed silylative pinacol coupling of carbonyl compound is observed for the first time and some hypotheses about the reaction mechanism are given.     

Novel and efficient Ni-mediated pinacol coupling of carbonyl compounds

It was firstly found that the Rieke Ni generated in situ was able to promote the pinacol coupling of various carbonyls efficiently. Based on this information, another catalytically effective, cheaper and more convenient NiCl₂(Cat.)/Mg/TMSCl system was designed and developed further successfully. The interesting single-electron transfer (SET) mechanisms for the coupling reactions were proposed. Additionally, the dl/meso diastereoselectivity and some additive effects were also explained in terms of the proposed mechanisms.     

Chromium(II)-catalyzed diastereoselective pinacol type cross coupling: studies of substrate-controlled effects

Using 20 mol % of CrCl₂ as catalyst, manganese powder as reducing agent, and TMS-Cl as scavenger, various acroleins and aldehydes were coupled with moderate to high yields and diastereomeric excesses. Alkyl aldehydes usually favor syn configuration while aldehydes with functional groups containing chelating hetero atoms promote the formation of anti configuration. Using sterically demanding alkyl residues on the acrolein substrate, the syn configuration is definitely preferred.     

On the paradox of TiCl4 reducing power: pinacol coupling and two-carbon homologation of carbonyl compounds

TiCl₄/DIPEA/CH₂Cl₂ reducing system promotes pinacol coupling and/or reduction to alcohol of aromatic aldehydes and carbonyl compounds activated towards reduction by an electron withdrawing group. In addition, bis homologation of these substrates is observed. An inner-sphere electron transfer from TiCl₄ to DIPEA accounts for the products distribution.     

Synthesis of N-heterocyclic diols by diastereoselective pinacol coupling reactions

A series of 5-8 membered N-heterocyclic diols have been prepared from acyclic dicarbonyls via diastereoselective pinacol reactions whereby cis- or trans-diol stereoselectivity is controlled by the choice of low-valent metal reagent used.     

InCl3/Al mediated pinacol coupling reactions of aldehydes and ketones in aqueous media

A systematic work on the homo-pinacol coupling reactions of benzophenones, aldehydes, and acetophenones in aqueous media with InCl₃/Al is described for the first time, in which various 1,2-diols are obtained in moderate to good yields.     

Influence of chelating silyl scavengers on the diastereoselectivity of chromium catalyzed pinacol cross couplings

The choice of the silyl scavenger shows a substantial influence on the diastereoselectivity of the chromium catalyzed pinacol cross coupling. In the case of the intramolecular cyclization, two competing effects are observed. If the silylation reagents contain chelating heteroatoms in the side chain, a remarkable trans-selectivity is observed. Conversely the cis-diols are preferred if bulky substituted scavengers are used. A suitable transition state model for this reaction is reported, based on formerly published results.     

A new preparation of samarium dibromide and its use in stoichiometric and catalytic pinacol coupling reactions

A new convenient preparation of samarium dibromide in THF is reported. Pinacol coupling reactions using SmBr₂ in catalytic amounts together with mischmetall as a coreductant have been performed with a variety of carbonyl compounds.     

TiCl4-Mg介导的立体选择性的频哪醇偶联反应研究

以ＴｉＣｌ４－Ｍｇ和ＴｉＣｌ４－Ｍｇ－ＴＭＥＤＡ为偶联剂实现对芳香醛高非对映选择性的还原偶联反应。以３种类型的手性试剂对ＴｉＣｌ４－Ｍｇ系统进行修饰,对苯甲醛的反应最高可得到５０％对映体过量的偶联产物。     

Enantiomerically Pure Cyclic trans-1,2-Diols,Diamines, and Amino Alcohols by Intramolecular Pinacol Coupling of Planar Chiral Mono-Cr(CO)3 Complexes of Biaryls

Without any formation of stereoisomers , the intramolecular pinacol cyclization of 1 —planar chiral mono-Cr(CO)₃ complexes of 1,1′-biphenyls with carbonyl functionalities at the 2- and 2′-positions—with samarium diiodide gives cyclic trans-1,2-diols 2 . Upon exposure to sunlight, the chromium-complexed diols 2 produce optically pure chromium-free trans-diols 3 . Similarly, the corresponding enantiomerically pure trans-1,2-diamines and amino alcohols are obtained from the planar chiral chromium complexes of biphenyls with diimino or keto-imino functionalities. R¹=H, OMe; R²=H, Me; R³=H, Me.     

Aerobic ligand-free Suzuki coupling catalyzed by in situ-generated palladium nanoparticles in water

A simple and efficient procedure for Suzuki coupling of aryl bromides/iodides with aryl- and alkylboronic acids catalyzed by in situ-generated palladium(0) nanoparticles in water without any ligand in open air to produce a variety of functionalized biaryls and alkyl-aryls has been developed. The boronic acids act here as the reducing agent for the formation of Pd nanoparticles. The reactions are remarkably fast (5 min) and high yielding. The catalyst is recyclable up to three runs without loss of efficiency.     

氢键的协同作用驱动水中苯甲醛的合成

以环氧氯丙烷作为交联溶剂合成和表征了纤维素功能化的β-环糊精,考察了这种超分子聚合物作为一种多相催化剂用于苯甲醛的合成的催化性能. 结果表明,该催化剂在温和的反应条件下具有较高的催化活性和选择性,容易恢复和重新利用,且活性没有大的损失. 进一步研究指出,β-环糊精聚合物中的b-环糊精能通过非极性共价键与肉桂醛形成主客包结物,此外,β-环糊精和纤维素的功能基团能与肉桂醛通过O-H…O的氢键形成多重氢键的相互作用,这种氢键的协同作用明显提高了催化剂的性能.     

Reduction and coupling reaction of carbonyl compounds by KI/Fe(OH)3 in aqueous media

ABSTRACT

A small amount of ferric hydroxide was found to catalyze KI-activated coupling of aromatic aldehydes and acetophenone to give the corresponding pinacols in high yields. The ratio of meso to dl isomer was approximately 1:1. Most aliphatic aldehydes and ketones were unreactive under the same conditions.     

Nanoparticle-catalyzed green synthetic chemistry … in water

Pre-catalyst nanoparticles (NPs) can be derived from FeCl₃ and methyl Grignard that contain ppm levels of Pd and an associated ligand. By varying the amount of precious metal and the nature of the phosphine ligand, different C–C bond-forming reactions can be catalyzed in an aqueous medium containing very small amounts (2 wt %) of the designer surfactant TPGS-750-M. Reactions mediated by these NPs include Suzuki–Miyaura, Sonogashira, Mizoroki–Heck, and Negishi couplings, as well as other couplings that have appeared in the recent literature. Also included in the discussion are nitro group reductions that require even less Pd and no ligand for activity, as well as ppm Cu-containing NPs that catalyze click reactions in water at rt.     

Dynamic nuclear magnetic resonance spectroscopic studies of (2.2.1)-cryptand incorporating a pinacol unit

The conformational behaviour of the (2.2.1)-cryptand framework has been studied by VT¹H and¹³C NMR spectroscopy, revealing a remarkable rigidity of the skeleton. Low-temperature measurements indicate a slowing down of the torsional motion of the methyl groups about the C–C bond in the pinacol unit with G =46 kJ mol^–1 at 228 K.Presented at the International Seminar on Inclusion Compounds, Jaszowiec, Poland, 24–26 September 1987.     

水相中钯催化碘代芳烃Ullmann偶联反应研究

研究了吸电子基团的贫电碘代芳烃的Ullmann偶联反应,该反应使用Pd(OAc)2为催化剂,K2CO3为添加剂,以丙酮-水混合液为溶剂,不需要添加额外的还原剂,收率为55-87%。在通过了一系列的试验后,可以认为该反应中的溶剂及碱没有起还原作用,而是碘代芳烃自身作为还原剂,完成整个催化反应的,并首次提出了一种不需要外加还原剂的Pd(II)/Pd(IV)/Pd(II)的催化循环机理。     

Study on improved diastereoselectivity in photo-induced electron transfer pinacol coupling reactions of substituted acetophenones

Novel diastereoselective photo-induced pinacol coupling reactions of acetophenones by using triethylamine and chiral tertiary amines as electron donating co-sensitizers were studied. Various influence factors including solvents, substituents, and chiral amines on both the diastereoselectivity and yield were examined. The diastereoselectivities were enhanced in supramolecular systems of cyclodextrins and zeolites. The best result of dl/meso up to 82:18 was obtained in combination use of chiral tertiary amine and β-CD.     

Synthesis of three-dimensionally arranged bis-biphenol ligand on hexaaryl benzene scaffold and its application for cross-pinacol coupling reaction

The three-dimensionally arranged bis-biphenol ligand on a hexaaryl benzene scaffold for a dinuclear complex was synthesized by the Diels-Alder addition-decarbonylation reaction as a key step. Its preliminary studies on the titanium-induced cross-pinacol coupling reaction were performed based on step-by-step activation of two different aldehydes.