An efficient chemo and regioselective oxidative nuclear bromination of activated aromatic compounds using lithium bromide and ceric ammonium nitrate

TBAX/Oxone-Mediated Halogenation of Pyrazoles and Other Heterocycles: An Entry to Important Cross-Coupling Reactions

A facile, sustainable and eco-friendly protocol has been developed for the halogenation of various heterocycles using TBAX (TBAI/TBAB/TBACl) as halogenating agent, which afforded the products in 90-95% isolated yields. The reaction proceeds with low-cost TBAX and uses greener conditions like EtOH as a solvent and microwave as an alternative energy source for reaction. This protocol has been applied on pyrazoles and extended to different heterocycles like 7-azaindole, indazole, indole and 2-phenylimidazo[1,2-α]pyridines. The gram-scale iodination reaction has also been successfully performed by optimizing conventional heating conditions, which demonstrates its potential applicability in organic synthesis. Further these halogenated pyrazoles have been utilized for different coupling reactions including formation of arylated, alkynylated and sulfenated pyrazoles. However, TBAF mediated fluorination did not work.

Automated grindstone chemistry: a simple and facile way for PEG-assisted stoichiometry-controlled halogenation of phenols and anilines using N-halosuccinimides

A simple electrical mortar–pestle was used for the development of a green and facile mechanochemical route for the catalyst-free halogenation of phenols and anilines via liquid-assisted grinding using PEG-400 as the grinding auxiliary. A series of mono-, di-, and tri-halogenated phenols and anilines was synthesized in good to excellent yields within 10–15 min in a chemoselective manner by controlling the stoichiometry of N-halosuccinimides (NXS, X = Br, I, and Cl). It was observed that PEG-400 plays a key role in controlling the reactivity of the substrates and to afford better regioselectivity. Almost exclusive para-selectivity was observed for the aromatic substrates with free o- and p-positions for mono- and dihalogenations. As known, the decarboxylation (or desulfonation) was observed in the case of salicylic acids and anthranilic acids (or sulfanilic acids) leading to 2,4,6-trihalogenated products when 3 equiv of NXS was used. Simple instrumentation, metal-free approach, cost-effectiveness, atom economy, short reaction time, and mild reaction conditions are a few noticeable merits of this environmentally sustainable mechanochemical protocol.

Eco-Friendly Methodology for the Formation of Aromatic Carbon-Heteroatom Bonds by Using Green Ionic Liquids

A new sustainable method is reported for the formation of aromatic carbon-heteroatom bonds under solvent-free and mild conditions (no co-oxidant, no strong acid and no toxic reagents) by using a new type of green ionic liquid. The bromination of methoxy arenes was chosen as a model reaction. The reaction methodology is based on only using natural sodium bromine, which is transformed into an electrophilic brominating reagent within an ionic liquid, easily prepared from the melted salt FeCl₃ hexahydrate. Bromination reactions with this in-situ-generated reagent gave good yields and excellent regioselectivity under simple and environmentally friendly conditions. To understand the unusual bromine polarity reversal of sodium bromine without any strong oxidant, the molecular structure of the reaction medium was characterised by Raman and direct infusion electrospray ionisation mass spectroscopy (ESI-MS). An extensive computational investigation using density functional theory methods was performed to describe a mechanism that suggests indirect oxidation of Br^- through new iron adducts. The versatility of the methodology was successively applied to nitration and thiocyanation of methoxy arenes using KNO₃ and KSCN in melted hexahydrated FeCl₃ .

Transition metal free, green and facile halogenation of ketene dithioacetals using a KX–oxidant system

A facile oxidative halogenation of α-oxo ketene dithioacetals is achieved by using a potassium halide and an oxidant combination under transition metal free conditions at ambient temperature.

Mild and Regioselective Oxidative Bromination of Aromatic Compounds Using Ammonium Bromide and Oxone®

The selective mono-bromination of various activated aromatic compounds is reported using in situ generated bromine from NH4Br as a bromine source and oxone® as an oxidant for the first time.

A quick, mild and efficient bromination using a CFBSA/KBr system

A quick, mild and efficient oxidative bromination by using CFBSA/KBr system has been developed. It was successfully applied into four different types of compounds including, 1,3-diketones and β-keto esters, aromatic amines, phenols and heteroarenes.

Total syntheses of multicaulins via oxidative photocyclization of stilbenes

The Wittig reaction of 3-isopropyl-4-methoxybenzaldehyde and 2,3-dimethylbenzylphosphonium bromide afforded the corresponding stilbene mixture 16. Oxidative photocyclization of stilbene 16 with iodine facilitated the first total synthesis of 7-isopropyl-6-methoxy-1,2-dimethylphenanthrene, multicaulin (1). The O-demethylation of 1 with BBr3 afforded the 7-isopropyl-1,2-dimethylphenanthren-6-ol, O-demethylmulticaulin (2).

Regioselective electrophilic aromatic bromination: theoretical analysis and experimental verification

Electrophilic aromatic bromination is the most common synthetic method used to prepare aryl bromides, which are very useful intermediates in organic synthesis. To understand the experimental results in electrophilic aromatic brominations, ab initio calculations are used here for a tentative analysis of the positional selectivity. The calculated results agree well with the corresponding experimental data, and the reliability of the resulting positional selectivity was verified by the corresponding experimental data.

Monobromomalononitrile: an efficient regioselective mono brominating agent towards active methylene compounds and enamines under mild conditions

The potential of monobromomalononitrile (MBM) as a convenient source of cationic bromine in organic bromination reaction has been explored.

Simple and improved regioselective brominations of aromatic compounds using N-benzyl N,N-dimethyl anilinium peroxodisulfate in the presence of potassium bromide under mild reactions conditions

A simple, efficient, and mild method for the selective bromination of some activated aromatic compounds using N-benzyl N,N dimethyl anilinium peroxodisulfate in the presence of potassium bromide in non-aqueous solution is reported. The results obtained revealed good to excellent selectivity between the ortho and para positions of phenols and methoxyarenes.