Microwave Assisted Esterification of Aryl/Alkyl Acids Catalyzed by N-Fluorobenzenesulfonimide

The susceptibility of the carbonyl group towards nucleophilic attack affords the construction of various organic compounds. Thus, investigations of carbonyl activation applying greener methodologies are highly important. In the present work, among the investigated N-halo compounds, N-fluorobenzenesulfonimide (NFSi) has been found as an efficient and selective catalyst in the reaction of direct esterification of aryl and alkyl carboxylic acids supported by microwave (MW) irradiation. The comprehensive esterification of different benzoic acids and mono-, di- and tri-carboxy alkyl derivatives was performed, whereby significant reaction time reductions were achieved. The presented method used NFSi as an easily manipulatable, non-metal, water- and air-tolerant catalyst, allowing simple synthetic and isolation procedures and energy saving, compared to conventional methodologies. Importantly, in contrast to esterification under thermal conditions, where N-halo compounds behave as pre-catalysts, in the MW-supported protocol, a distinct reaction mechanism has been proposed that assumes NFSi as a sustainable catalyst. Moreover, a scale-up of the industrially important derivative was performed.

Mahardhika A, L. Wendt L, E. Müller C. Iodine-catalyzed electrophilic substitution of indoles: Synthesis of (un)symmetrical diindolylmethanes with a quaternary carbon center

A novel, versatile approach for the synthesis of unsymmetrical 3,3'-diindolylmethanes (DIMs) with a quaternary carbon center has been developed via iodine-catalyzed coupling of trifluoromethyl(indolyl)phenylmethanols with indoles. In contrast to previously reported methods, the new procedure is characterized by chemoselectivity, mild conditions, high yields, and scalability to obtain gram amounts for biological studies. Selected compounds were found to display affinity for cannabinoid receptors, which are promising drug targets for the treatment of inflammatory and neurodegenerative diseases.

Rapid access to indole-fused bicyclo[2.2.2]octanones by merging the umpolung strategy and molecular iodine as a green catalyst

One-pot synthesis of indole-fused bicyclo[2.2.2]octanones from DiMeOIN and 2-cyclohexen-1-one is accomplished under an iodine catalyst. The simple and metal-free conditions provide a practical tool to construct Csp3-rich complex molecules via coupling cyclization.

Revisiting applications of molecular iodine in organic synthesis

Molecular iodine contributes significantly to organic transformations in synthetic organic chemistry. It works effectively due to its mild Lewis acidic character, ability as an oxidizing agent, good moisture stability, and easy availability.

N-Iodosuccinimide as a Precatalyst for Direct Cross-Coupling of Alcohols with C-Nucleophiles under Solvent-Free Reaction Conditions

C–C bond formation is one of the most important implements in synthetic organic chemistry. In pursuit of effective synthetic routes functioning under greener pathways to achieve direct C–C bond formation, we report N-iodosuccinimide (NIS) as the most effective precatalyst among the N-halosuccinimides (NXSs) for the direct cross-coupling of benzyl alcohols with C-nucleophiles under solvent-free reaction conditions (SFRC). The protocol is metal-free, and air- and water-tolerant, providing a large-scale synthesis with almost quantitative yields.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.

Molecular Iodine-Catalyzed Selective C-3 Benzylation of Indoles with Benzylic Alcohols: A Greener Approach toward Benzylated Indoles

Iodine-catalyzed selective C-3 benzylation of indoles with benzylic alcohols is developed. The reaction proceeds with molecular iodine as the catalyst under ligand-, metal-, and base-free conditions and tolerates wide functionalities. The experimental observations account for the halogen-bond activation mechanistic pathway for the molecular iodine catalysis.

1,3-Dibromo-5,5-dimethylhydantoin as a Precatalyst for Activation of Carbonyl Functionality

Activation of carbonyl moiety is one of the most rudimentary approaches in organic synthesis and is crucial for a plethora of industrial-scale condensation reactions. In esterification and aldol condensation, which represent two of the most important reactions, the susceptibility of the carbonyl group to nucleophile attack allows the construction of a variety of useful organic compounds. In this context, there is a constant need for development of and improvement in the methods for addition-elimination reactions via activation of carbonyl functionality. In this paper, an advanced methodology for the direct esterification of carboxylic acids and alcohols, and for aldol condensation of aldehydes using widely available, inexpensive, and metal-free 1,3-dibromo-5,5-dimethylhydantoin under neat reaction conditions is reported. The method is air- and moisture-tolerant, allowing simple synthetic and isolation procedures for both reactions presented in this paper. The reaction pathway for esterification is proposed and a scale-up of certain industrially important derivatives is performed.