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Structural Design for Molecular Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Qingmin Ji, Qin Tang, Jonathan P. Hill, Katsuhiko Ariga
Although proline continues to play a central role in amino-catalysis, its supremacy can also be reflected by the facial synthesis for more complex proline derivatives. Both Barbas et al. and Hayashi et al. independently reported amine-derived chiral catalysts capable of inducing high enantiocontrol in the presence of large excess of water [89–90]. In their cases, highly hydrophobic proline derivatives have been used as catalysts for direct aldol reactions. Itoh et al. synthesized a series of N-substituted prolines and studied the catalytic performance for the asymmetric reduction of imines with trichlorosilane [91]. The reduction of N-aryl imines in the presence of 10 mol% N-pivaloyl-L-proline anilide was shown to give the corresponding amines in excellent yields (up to 99%) and with high enantioselectivities (up to 93% ee). Since the catalyst could interact with the substrate imine, the Lewis base proline catalyst could coordinate with trichlorosilane and activate the reducing agent in a synergistic manner. It was suggested that the coordination between Si and O atom of the amide group, and hydrogen bonding between the imine nitrogen and anilide hydrogen promotes the asymmetric reaction. It thus resulted in the attack from the Re face of the imine to give the optically active (S) amine.
Surface Acidity and Catalytic Activity
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
Interestingly, arene radical-cations can polymerize in organic solvents, and even in an aqueous environment (Cloos et al. 1979; Moreale et al. 1985; Faguy et al. 1995). For example, when an aqueous aniline solution was percolated through a sand column containing Fe3+-montmorillonite, colored streaks and spots were visible along the column, indicative of type II complex formation. Treating the separated complex with 0.1 M HCl or alkaline Na4P2O7 did not change its color nor its carbon content, a behavior not unlike that shown by soil humin or kerogen (Cloos et al. 1981). Likewise, the soil-catalyzed conversion of aniline to yield azobenzene, azoxybenzene, phenazine, anilide, and acetanilide, reported by Pillai et al. (1982), is indicative of an oxidation process involving ferric ions.
The Synthesis and Properties of New Oxygen- and Nitrogen- Containing Terpene Acid Derivatives
Published in Alexander V. Kutchin, Lyudmila N. Shishkina, Larissa I. Weisfeld, Gennady E. Zaikov, Ilya N. Kurochkin, Alexander N. Goloshchapov, Chemistry and Technology of Plant Substances, 2017
Maksim P Bei, Anatolij P Yuvchenko
The method of A-(aryl)aralkyl MPA imido amides 24a-k synthesis from aromatic amides 14c-e, k and amines (aniline, p-toluidine, p-anisi- dine, p-fluoro-, p-chloro-, p-bromoaniline, benzylamine, and 2-pycolyl- amine) was developed (Fig. 3.13) [38]. Optimum reaction conditions were established as: molar ratio amide:amine 1:3, refluxing in p-xylene for 40 h. The yields of imido amides 24a-k reach 41-94%. The conducting of this reaction at lower temperatures (refluxing in toluene), and the use of only 20-100% excess of amine led to the substantial decrease of target product yields. For example, reaction of MPA anilide 14k with aniline (molar ratio 1:1.2, refluxing in toluene for 40 h) gave imido amide 24a with only 20% yield, and when the solvent was replaced by p-xylene, the imido amide 24a was prepared with 31% yield. The use of 100% excess of aniline (refluxing in p-xylene for 40 h) gave imido amide 24a with 50% yield, and only the use of three equivalents of aniline allowed synthesizing imido amide 24a with 70% yield. The increase of imido amide yield with the increase of amine excess is probably due to higher concentration of amine and polarity of reaction system [39].
An expedient and rapid green chemical synthesis of N-chloroacetanilides and amides using acid chlorides under metal-free neutral conditions
Published in Green Chemistry Letters and Reviews, 2018
Finally, to expand the scope of this process we prepared various amides/anilides by condensation of amines/anilines with different acid chlorides. The results were reported in Table 3. Many structurally diverse amides were formed with ease using this protocol. Individually aliphatic or aromatic amines can be reacted with aliphatic or aromatic acid chlorides to yield the corresponding amide/anilide derivatives in high yields. We used aliphatic (Table 3, entries 2, 4–6, 12, 15, 17, 21), aromatic (Table 3, entries 1, 7, 9–11, 13, 14), α, β-unsaturated (Table 3, entries 8, 22), cyclic (Table 3, entry 18), and heterocyclic (Table 3, entries 23, 24) acid chlorides. We also varied the electrophilic nature (Table 3, entries 3, 16, 19, 20) of the substituent on the acid chloride. For the amine part we have used anilines (Table 3 entries 1–6, 9–11, 13–18, 20, 23) and amines (Table 3, entries 7, 8, 12, 19, 21, 22, 24). In all cases, we observed the required amide formation. The isolated yields of the obtained anilides were excellent in most cases. Even the dicarboxyl chloride (Table 3, entries 13, 14) underwent the reaction smoothly. Electron-withdrawing groups on the aniline (Table 3, entry 11) or on the acid chloride (Table 3, entries 3, 9–11, 16) did not affect the product formation. The current protocol of using buffers as a solvent is highly beneficial, because (i) we can avoid the use of toxic organic solvents, (ii) we can isolate the product with ease. Due to the poor solubility of the product in the reaction medium, they can be easily isolated by simple precipitation/filtration. This completely avoids the laborious column chromatography procedure for purification of the products (Figure 2).