3824-74-6Relevant academic research and scientific papers
Exploiting molecular self-assembly: From urea-based organocatalysts to multifunctional supramolecular gels
Schoen, Eva-Maria,Marques-Lopez, Eugenia,Herrera, Raquel P.,Aleman, Carlos,Diaz, David Diaz
, p. 10720 - 10731 (2014)
We describe the self-assembly properties of chiral N,N′-disubstituted urea-based organocatalyst 1 that leads to the formation of hierarchical supramolecular gels in organic solvents at low concentrations. The major driving forces for the gelation are hydr
Na+ Ions Induce the Pirouetting Motion and Catalytic Activity of [2]Rotaxanes
Lee, Yong-Jay,Liu, Kuang-Shun,Lai, Chien-Chen,Liu, Yi-Hung,Peng, Shie-Ming,Cheng, Richard P.,Chiu, Sheng-Hsien
, p. 9756 - 9760 (2017)
We have prepared [2]rotaxanes, the behavior of which as switchable catalysts depends on their pirouetting motion, which can be controlled through the addition and removal of Na+ ions. At least three sequential on/off cycles of a Michael reactio
Self-assembled bimetallic aluminum-salen catalyst for the cyclic carbonates synthesis
Abboud, Khalil A.,Hahm, Hyungwoo,Hong, Sukwon,Kim, Seyong,Park, Jongwoo,Seong, Wooyong
supporting information, (2021/07/21)
Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO2. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst. The bimetallic reaction pathway is suggested based on urea additive studies and kinetic studies. Additionally, the X-ray crystal structure of a bis-urea salen Ni complex supports the self-assembly of the bis-urea salen metal complex through hydrogen bonding.
Hydrogen-Bond Catalysis of Imine Exchange in Dynamic Covalent Systems
Schaufelberger, Fredrik,Seigel, Karolina,Ramstr?m, Olof
supporting information, p. 15581 - 15588 (2020/10/02)
The reversibility of imine bonds has been exploited to great effect in the field of dynamic covalent chemistry, with applications such as preparation of functional systems, dynamic materials, molecular machines, and covalent organic frameworks. However, acid catalysis is commonly needed for efficient equilibration of imine mixtures. Herein, it is demonstrated that hydrogen bond donors such as thioureas and squaramides can catalyze the equilibration of dynamic imine systems under unprecedentedly mild conditions. Catalysis occurs in a range of solvents and in the presence of many sensitive additives, showing moderate to good rate accelerations for both imine metathesis and transimination with amines, hydrazines, and hydroxylamines. Furthermore, the catalyst proved simple to immobilize, introducing both reusability and extended control of the equilibration process.
Urea-Catalyzed Vinyl Carbocation Formation Enables Mild Functionalization of Unactivated C-H Bonds
Bagdasarian, Alex L.,Popov, Stasik,Wigman, Benjamin,Wei, Wenjing,Lee, Woojin,Nelson, Hosea M.
supporting information, p. 7775 - 7779 (2020/07/15)
Herein we report the 3,5-bistrifluoromethylphenyl urea-catalyzed functionalization of unactivated C-H bonds. In this system, the urea catalyst mediates the formation of high-energy vinyl carbocations that undergo facile C-H insertion and Friedel-Crafts re
Zinc Powder Catalysed Formylation and Urealation of Amines Using CO2 as a C1 Building Block?
Du, Chongyang,Chen, Yaofeng
, p. 1057 - 1064 (2020/06/30)
Transformation of CO2 into valuable organic compounds catalysed by cheap and biocompatible metal catalysts is one of important topics of current organic synthesis and catalysis. Herein, we report the zinc powder catalysed formylation and urealation of amines with CO2 and (EtO)3SiH under solvent free condition. Using 2 molpercent zinc powder as the catalyst, a series of secondary amines, both the aromatic ones and the aliphatic ones, can be formylated into formamides. When primary aromatic amines were used as the substrates, the reactions produce urea derivatives. The electronic and steric effects from the substrates on the formylation and urealation reactions were observed and discussed. The recovery and reusability of zinc powder were investigated, showing the zinc powder can be reused in the formylation reaction without loss of catalytic activity. The analysis on the reactants/products mixture after filtering out the zinc powder showed the zinc concentration in the mixture is low to 1 ppm. The pathways for the formylation and urealation of amines with this catalytic system were also investigated, and related to the different substrates.
Synthesis of glycosyl chlorides using catalytic Appel conditions
Pongener, Imlirenla,Nikitin, Kirill,McGarrigle, Eoghan M.
supporting information, p. 7531 - 7535 (2019/08/20)
The stereoselective synthesis of glycosyl chlorides using catalytic Appel conditions is described. Good yields of α-glycosyl chlorides were obtained using a range of glycosyl hemiacetals, oxalyl chloride and 5 mol% Ph3PO. For 2-deoxysugars treatment of the corresponding hemiacetals with oxalyl chloride without phosphine oxide catalyst also gave good yields of glycosyl chloride. The method is operationaly simple and the 5 mol% phosphine oxide by-product can be removed easily. Alternatively a one-pot, multi-catalyst glycosylation can be carried out to transform the glycosyl hemiacetal directly to a glycoside.
Mechanism-Based Condition Screening for Sustainable Catalysis in Single-Electron Steps by Cyclic Voltammetry
Liedtke, Theresa,Spannring, Peter,Riccardi, Ludovico,Gans?uer, Andreas
supporting information, p. 5006 - 5010 (2018/03/30)
A cyclic-voltammetry-based screening method for Cp2TiX-catalyzed reactions is introduced. Our mechanism-based approach enables the study of the influence of various additives on the electrochemically generated active catalyst Cp2TiX, which is in equilibrium with catalytically inactive [Cp2TiX2]?. Thioureas and ureas are most efficient in the generation of Cp2TiX in THF. Knowing the precise position of the equilibrium between Cp2TiX and [Cp2TiX2]? allowed us to identify reaction conditions for the bulk electrolysis of Cp2TiX2 complexes and for Cp2TiX-catayzed radical arylations without having to carry out the reactions. Our time- and resource-efficient approach is of general interest for the design of catalytic reactions that proceed in single-electron steps.
Urea anions: Simple, fast, and selective catalysts for ring-opening polymerizations
Lin, Binhong,Waymouth, Robert M.
supporting information, p. 1645 - 1652 (2017/02/10)
Aliphatic polyesters and polycarbonates are a class of biorenewable, biocompatible, and biodegradable materials. One of the most powerful methods for accessing these materials is the ring-opening polymerization (ROP) of cyclic monomers. Here we report that the deprotonation of ureas generates a class of versatile catalysts that are simultaneously fast and selective for the living ring-opening polymerization of several common monomers, including lactide, δ-valerolactone, ε-caprolactone, a cyclic carbonate, and a cyclic phosphoester. Spanning several orders of magnitude, the reactivities of several diaryl urea anions correlated to the electron-withdrawing substituents on the aryl rings. With the appropriate urea anions, the polymerizations reached high conversions (～90%) at room temperature within seconds (1-12 s), yielding polymers with narrow molecular weight distributions (Crossed D sign = 1.06 to 1.14). These versatile catalysts are simple to prepare, easy to use, and exhibit a range of activities that can be tuned for the optimal performance of a broad range of monomers. (Chemical Equation Presented).
Stereoselective Koenigs–Knorr Glycosylation Catalyzed by Urea
Sun, Lifeng,Wu, Xiaowei,Xiong, De-Cai,Ye, Xin-Shan
supporting information, p. 8041 - 8044 (2016/09/13)
A stereoselective Koenigs–Knorr glycosylation reaction under the catalysis of urea is described. This method is characterized by urea-mediated hydrogen-bond activation and subsequent glycosylation with glycosyl chlorides or bromides. Excellent yields and high anomeric selectivity can be achieved in most cases. Moreover, the low α-stereoselectivity of glycosylations observed when using perbenzylated glucosyl donors can be greatly improved by the addition of tri-(2,4,6-trimethoxyphenyl)phosphine (TTMPP).
