A Catalyst-Controlled Enantiodivergent Bromolactonization.

A catalyst-controlled enantiodivergent bromolactonization of olefinic acids has been developed. Quinine-derived amino-amides bearing the same chiral core but different achiral aryl substituents were used as the catalysts. Switching the methoxy substituent in the aryl amide system from meta- to ortho-position results in a complete switch in asymmetric induction to afford the desired lactone in good enantioselectivity and yield. Mechanistic studies, including chemical experiments and density functional theory calculations, reveal that the differences in steric and electronic effects of the catalyst substituent alter the reaction mechanism.

Zwitterion-Catalyzed Isomerization of Maleic to Fumaric Acid Diesters.

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 Deacylative Dihalogenation of ß-Oxo Amides.

α,α-Dihalo-N-arylacetamides are commonly used as intermediates in various organic reactions. In the study described here, a catalytic synthesis of α,α-dihalo-N-arylacetamides from ß-oxo amides was developed using zwitterionic catalysts and N-halosuccinimides as the halogen sources. The corresponding α,α-dihalo-N-arylacetamides were obtained in good to excellent yields, and no aromatic halogenated side products were detected. The reaction conditions were mild, and no strong base or acid was required.

Zwitterion-Catalyzed Intermolecular Bromoesterifications.

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.

Metal-Free Allylic Oxidation of Steroids Using TBAI/TBHP Organocatalytic Protocol.

A mild, efficient and organocatalytic allylic oxidation of steroids using a TBAI/TBHP protocol has been developed. A range of bioactive Δ5 -en-7-ones can be easily prepared from the corresponding Δ5 -steroids. The methodology features several advantages, including readily available starting materials, environmentally benign oxidant, high functional group compatibility, and metal-free catalysis.