Stojan Stavber

Bromination of ketones with H2O2–HBr “on water”

Various 1,3-diketones, β-ketoesters, cyclic ketones, aryl alkyl and dialkyl ketones were effectively brominated with an aqueous H2O2–HBr system “on water” at room temperature without the need for a catalyst or organic solvent. The resultant brominated ketones were isolated in yields of 69–97% with high selectivity for monobromination vs. dibromination. Reactivity was manipulated by using more diluted aqueous solutions of H2O2 and HBr and the use of an excess of HBr where necessary. Dilution also increases selectivity of ring bromination vs. α-bromination of aryl ketones with an activated phenyl ring. Finally, an aqueous H2O2–HBr system was used for a tandem oxidation–bromination process and alcohols were transformed into α-bromoketones. This simple but effective “on water” bromination of ketones with an aqueous H2O2–HBr system is characterised by the use of inexpensive reagents, a lower impact on the environment and the absence of organic waste that make it a good alternative to existing bromination methods.

Selective aerobic oxidative dibromination of alkenes with aqueous HBr and sodium nitrite as a catalyst

Various alkenes (internal, terminal, aryl and alkyl substituted) and 1,2-diphenylethyne were efficiently and selectively dibrominated using 2 equivalents of 48% aqueous hydrobromic acid, with air as an oxidant and sodium nitrite as a catalyst. Despite the presence of water, only trans dibromination occurred producing anti-1,2-dibromoalkanes and (E)-1,2-dibromo-1,2-diphenylethene. A comparison of resource demand, waste production and environmental, health and safety issues of the NaNO2 catalyzed aerobic bromination with molecular bromine and other oxidative bromination methods revealed that the proposed method is not only selective and effective but has a better environmental profile.

High yield direct fluorofunctionalisation of ketones using AccufluorTM-NFTh fluorinating reagent

Abstract Direct regioselective conversion of a variety of cyclic and acyclic ketones to α-fluoroketones was achieved in high to excellent yield using 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2,2,2]octane bis(tetrafluoroborate) [AccufluorTM - NFTh] in acetonitrile solution.

Effective and selective iodofunctionalisation of organic molecules in water using the iodine–hydrogen peroxide tandem

Efficient hydrogen peroxide enhanced iodofunctionalisation of ketones, 1,3-dicarbonyl derivatives and activated aromatic molecules using elemental iodine in water is achieved, whereas alkynes were stereoselectively converted into (E)-1,2-diiodoalkenes.

Recent Advances in the Application of SelectfluorTMF-TEDA-BF4 as a Versatile Mediator or Catalyst in Organic Synthesis

SelectfluorTM F-TEDA-BF4 (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo [2.2.2]octane bis(tetrafluoroborate) is not only one of the most efficient and popular reagents for electrophilic fluorination, but as a strong oxidant is also a convenient mediator or catalyst of several “fluorine-free” functionalizations of organic compounds. Its applications as a mediator in transformations of oxidizable functional groups or gold-catalyzed C-C and C-heteroatom oxidative coupling reactions, a catalyst in formation of various heterocyclic rings, a reagent or catalyst of various functionalizations of electron-rich organic compounds (iodination, bromination, chlorination, nitration, thiocyanation, sulfenylation, alkylation, alkoxylation), a catalyst of one-pot-multi-component coupling reactions, a catalyst of regioselective ring opening of epoxides, a deprotection reagent for various protecting groups, and a mediator for stereoselective rearrangement processes of bicyclic compounds are reviewed and discussed.

Room Temperature Regioselective Iodination of Aromatic Ethers Mediated by SelectfluorTM Reagent F-TEDA-BF4

Abstract Monosubstituted phenyl ethers were regioselectively iodinated with a mixture of iodine and F-TEDA in acetonitrile at room temperature at the para position, while 1-methoxy-4-substituted benzene derivatives were converted to 2-iodo products in high yield.

1-Fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) as a new, effective reagent for selective fluorofunctionalisation of alkenes under mild reaction conditions

Abstract 1-Fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) ( Accufluor ™ NFTh) is confirmed as a highly effective reagent for introducing a fluorine atom into organic molecules across a phenyl-substituted carbon-carbon double bond. Quantitative and Markovnikov-type regioselective formation of vicinal fluoro-hydroxy, fluoro-methoxy or fluoro-acetoxy adducts was achieved when phenyl-substituted alkenes were treated with a MeCN solution of NFTh In the presence of water, methanol or acetic acid. The stereochemical course of fluoro-methoxylation reactions in the case of cyclic phenyl-substituted alkenes depends strongly on the structure of the alkene.

Solvent-free bromination of 1,3-diketones and β-keto esters with NBS

Trituration of N-bromosuccinimide at room temperature with several liquid or solid 1,3-diketones and β-keto esters resulted in high yield conversion to the monobrominated derivatives, and a work-up procedure using only water to remove succinimide was employed. The entire process uses no organic solvent and is therefore more ecologically desirable.

A mild, selective method for preparation of vicinal fluoro ethers using F-Teda-BF4

Vicinal alkoxy fluorides are efficiently formed by room temperature reaction of phenyl substituted alkenes with commercially available 1-chloromethyl-4-fluoro-1,4-diazobicyclo[2.2.2]octane bis tetrafluoroborate (Selectfluor™ F-Teda BF4) in CH3CN in the presence of various alcohols. The reaction follows Markovnikov-type regioselectivity, while stereoselectivity in the case of phenyl substituted benzocyclenes strongly depends on the ring size and the structure of the alcohol.

Aerobic oxidative iodination of ketones catalysed by sodium nitrite “on water” or in a micelle-based aqueous system

Selective and efficient aerobic oxidative iodination of ketones in aqueous media was achieved by using molecular iodine as the source of iodine atoms, air as the terminal oxidant, sodium nitrite (NaNO2) as the catalyst and H2SO4 as the activator of the overall catalytic process. The efficiency of the reaction, resulting in α-iodo ketones, was significantly improved in an aqueous solution of the anionic amphiphile sodium dodecyl sulfate (SDS), capable of self-assembly into micelle-based aggregates, thus forming a reactive micellar system. The regioselectivity of iodofunctionalization of aryl methyl ketones was regulated by the reaction medium used: in an aqueous micelle-based system the methyl group was iodinated, while in anhydrous MeCN aryl iodides were formed with high selectvity.