Zwitterion-Catalyzed Isomerization of Maleic to Fumaric Acid Diesters

Abstract

Fumaric acid diesters are important building blocks for organic synthesis. A class of zwitterionic organocatalysts based on an amide anion/iminium cation charge pair were found to be effective in catalyzing the isomerization of maleic acid diesters to give fumaric acid diesters. Comparison of the performance of different zwitterionic organocatalysts toward the reaction revealed that nonclassical hydrogen bonding was involved in the stabilization of the Michael adduct intermediate.

Zwitterion‐Catalyzed Amino‐Dibromination of Nitroalkenes: Scope, Mechanism, and Application to The Synthesis of Glycinamides

“…A possible catalytic cycle is proposed based on the experimental observations (Scheme 5). Based on our previous studies, [21,23] zwitterions 1 readily interact with acidic protons and electrophilic Br, and the counteranions (e. g. succinimide of NBS) could be stabilized by the cationic moieties of 1 by nonclassical hydrogen bond (NCHB). [26] Thus, we believe that equilibrium among zwitterion 1 d, succinimide, and NBS might exist during the reaction.…”

“…Complexation between 1 d and succinimide potentially via imide deprotonation and NCHB interaction might give the succinimide species A. [21,23] Based on the kinetics data, subsequent nucleophilic addition of succinimide anion to 2 a could possibly be the rate-determining step of the reaction, yielding the nitronate anion in species B. We rationalized that the acidic NÀ H proton in species B might exchange with NBS to give species C. [23,27] The close proximity of the Br and nitronate in species C could facilitate the bromination (against the polymerization via the intermolecular reaction between species B and nitroalkene 2 a) to give species D. Species D, which possesses an acidic α-proton to the nitro group, might be deprotonated by zwitterion 1 d followed by another α-bromination through species (D!E!F) to yield the desired dibromide product 3 a.…”

“…Recently, our group has successfully demonstrated the use of amide/iminium zwitterionic catalysts 1 a-1 c for transesterification, dehydrative esterification reactions, deacylative dihalogenations, and isomerization reactions of maleic acid diesters. [21] The structurally stable zwitterions (e. g. 1 a) was prepared simply by reacting aziridine and DMAP. By replacing DMAP with trialkylphosphines, the phosphonium zwitterions 1 d and 1 e were prepared [22] and applied in the catalytic intermolecular haloesterification and aerobic oxidation.…”

A New Approach Utilizing Aza-Michael Addition for Hydrolysis-Resistance Non-Ionic Waterborne Polyester

“…Because the catalytic activity of Ti(OBu) 4 was the higher than both TsOH and DBTDL, the Entry 2L was the largest in molecular weight, but the excessive degradation reactions of Ti(OBu) 4 during polymerization process resulted the darkest color of the sample [37]. Moreover, the catalysts play an important in the isomerization process, which was usually used to manufacture fumarate from maleate [40], and the different isomerization extent using different catalysts may be related to the nucleophilicity [41] and rigidity [42] of the catalyst. In general, TsOH was more suitable as a polycondensation reaction catalyst in this work.…”

Zwitterion-Induced Organic–Metal Hybrid Catalysis in Aerobic Oxidation

“…Recently, our group has developed a new class of aziridine-derived [N + -N – ] ZW1 and [P + -N – ] ZW2 zwitterions, which were found to be highly effective in catalyzing (trans)­esterification reactions, deacylative dihalogenation of β-oxo amides, intermolecular bromoesterification of alkenes, and isomerization of maleic acid esters . Mechanistic studies suggest that zwitterion-catalyzed reactions involve a synergistic activation mode involving the following: (1) the basic sulfonamide anion interacts with the electrophilies (H or Br); (2) the cationic moiety interacts with the carbonyl groups via a nonclassical hydrogen bond (NCHB), which involves the C–H···O noncovalent interaction between the α-C–H of the cation of zwitterion and the carbonyl oxygen of the substrate (Figure A).…”