Zwitterion-Catalyzed Intermolecular Bromoesterifications

Abstract

Intermolecular haloesterification is an important class of transformations. The resulting products are valuable building blocks. However, it is often necessary to use super-stoichiometric amount of acid in order to compensate the low reactivity. Herein, we report a zwitterion-catalyzed intermolecular bromoesterification using acid and olefin in an equimolar ratio. Mechanistic study revealed that the charge pair in the zwitterion works synergistically in activating both NBS and carboxylic acid.

Zwitterion-Catalyzed Isomerization of Maleic to Fumaric Acid Diesters

“…Very recently, our research team successfully developed a new class of amide/iminium zwitterions 1 , which can easily be prepared by reacting aziridines with various amines such as 4-pyrrolidylpyridine (PPY) . The analogue amide/phosphonium zwitterion can also be prepared using phosphines instead of amines . These zwitterions are stable, nonhygroscopic, and have structurally well-defined pockets, making them suitable as catalysts for chemical transformations.…”

Nitroxyl Catalysts for Six-Membered Ring Bromolactonization and Intermolecular Bromoesterification of Alkenes with Carboxylic Acids

“…However, it is difficult to control the halogenation chemoselectively because the halonium ion intermediate generated by the electrophilic addition of olefin on alkenes and halogen reagents is highly reactive and induces some side reactions . Recently, some catalytic halo-functionalizations have been achieved by designing elaborately organocatalysts. − Among them, Lewis base catalysts containing heteroatoms having an electron-donating nature, such as nitrogen, oxygen, sulfur, selenium, and phosphorus, are efficient at inducing the desired halo-functionalization (Scheme a). These Lewis base catalysts activate the halogen atom on the halogen reagent via noncovalent interaction to promote a chemoselective reaction.…”

“…These Lewis base catalysts activate the halogen atom on the halogen reagent via noncovalent interaction to promote a chemoselective reaction. In particular, Lewis base–acid cooperative catalysts have been designed as a bifunctional organocatalyst to activate both the halogen atom and the counteranion on the halogen reagent for bromocyclizations (Scheme b) . On the other hand, nitroxyl catalysts, including a nitroxyl radical catalyst bearing an unpaired electron and N -oxide catalyst bearing a zwitterion, have often been cited for their unique performance as an organocatalyst for fine catalytic transformations.…”

Solvent and catalyst-free bromofunctionalization of olefins using a mechanochemical approach

“…5 Well reported examples include bromocyclization reactions such as bromolactonization [6][7][8][9][10][11][12][13][14][15] and bromoetherication [16][17][18][19] as well as the more challenging intermolecular bromoesterication. [20][21][22][23][24][25][26] Because of the high polarity of the N-bromoimide reagents, polar solvents such as N,N-dimethylformamide and acetonitrile are oen required for good solvation which poses difficulties in the purication process. The use of relatively less polar solvents such as dichloromethane and chloroform are also commonly reported.…”