5063-03-6Relevant articles and documents
Thiourea versus the oxyanion hole as a double H-bond donor
Mu?iz, Francisco M.,Montero, Victoria Alcázar,Fuentes de Arriba, ángel L.,Simón, Luis,Raposo, César,Morán, Joaquín R.
, p. 5050 - 5052 (2008)
A novel receptor based on the 4,5-diamine-9,9-dimethylxanthene skeleton functionalised with triflamides has been developed and its hydrogen-bonding donor ability is examined and compared with that of thiourea groups. The novel receptor also shows its potential as an organocatalyst.
Synthesis of novel dendritic 2,2′-bipyridine ligands and their application to lewis acid-catalyzed diels-alder and three-component condensation reactions
Muraki, Takahito,Fujita, Ken-Ichi,Kujime, Masato
, p. 7863 - 7870 (2007)
(Chemical Equation Presented) A series of dendritic ligands with a 2,2′-bipyridine core was synthesized through the coupling of 4,4′-dihydroxy-2,2′-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf) 2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.
NMR study of diastereoisomerism of 2-(1-aminoethyl)bicyclo[2.2.1]heptane and its hydrochloride (deitiforin)
Tandura,Shumsky,Litvin,Kozlova,Shuvalova,Sharf,Kolesnikov
, p. 1014 - 1022 (2001)
The assignment of the signals for the H and C atoms of four diastereomers (without their separation) of 2-(1-aminoethyl)bicyclo[2.2.1]heptane (1) and its hydrochloride (2) (the antiviral drug deitiforin) was performed for the first time by two-dimensional 1H and 13C NMR spectroscopy. The effects of the substituent at position 2 of norbornane on the chemical shifts of the α-, β-, and γ-carbon atoms of the bicycle were examined using the increments for alkanes. The changes in the chemical shifts of the C(6) and C(7) atoms are substantially larger than those for the other C atoms, which made it possible to identify the exo and endo forms. Each of these forms exists as a mixture of two diastereomers. The effect of the positive charge of the N atom on the γ-protons, which are closely spaced, but separated by a number of covalent bonds, was considered on going from amine 1 to hydrochloride 2. Based on significant changes in shielding of these H atoms, the configurations of the asymmetric center in the CHMe(NH2) substituent of the diastereomers were established.
Rapid quantification of the activating effects of hydrogen-bonding catalysts with a colorimetric sensor
Huynh, Phuong N. H.,Walvoord, Ryan R.,Kozlowski, Marisa C.
, p. 15621 - 15623,3 (2012)
A sensor has been developed to quickly and simply assess the relative reactivity of different hydrogen-bonding catalysts. Specifically, blue-shifts seen upon treatment of H-bonding catalysts with the colorimetric compound 7-methyl-2-phenylimidazo[1,2-a]pyrazin-3(7H)-one correlate well to the K eq of binding to the sensor. The blue-shifts also show a high degree of correlation with relative rates in Diels-Alder reactions of methyl vinyl ketone and cyclopentadiene employing the H-bonding catalysts. The relevance of the sensor blue-shifts to the LUMO-lowering abilities of the H-bonding catalysts is discussed.
Bis-selenonium Cations as Bidentate Chalcogen Bond Donors in Catalysis
He, Xinxin,Wang, Xinyan,Tse, Ying-Lung Steve,Ke, Zhihai,Yeung, Ying-Yeung
, p. 12632 - 12642 (2021/10/21)
Lewis acids are frequently employed in catalysis but they often suffer from high moisture sensitivity. In many reactions, catalysts are deactivated because of the problem that strong Lewis acids also bond to the products. In this research, hydrolytically stable bidentate Lewis acid catalysts derived from selenonium dicationic centers have been developed. The bis-selenonium catalysts are employed in the activation of imine and carbonyl groups in various transformations with good yields and selectivity. Lewis acidity of the bis-selenonium salts was found to be stronger than that of the monoselenonium systems, attributed to the synergistic effect of the two cationic selenonium centers. In addition, the bis-selenonium catalysts are not inhibited by strong bases or moisture.
N-Heterocyclic Iod(az)olium Salts – Potent Halogen-Bond Donors in Organocatalysis
Boelke, Andreas,Kuczmera, Thomas J.,Lork, Enno,Nachtsheim, Boris J.
supporting information, p. 13128 - 13134 (2021/08/09)
This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono- and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon- and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3.
Preorganization: A Powerful Tool in Intermolecular Halogen Bonding in Solution
Voelkel, Martin H. H.,Wonner, Patrick,Huber, Stefan Matthias
, p. 214 - 224 (2020/03/10)
Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra- and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)-based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)-based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding.
