Radical catalyzed debromination of bromo-alkanes by formate in aqueous solutions via a hydrogen atom transfer mechanism (original) (raw)
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Tetrahedron Letters, 2006
An aqueous solution of hydrogen peroxide and hydrogen bromide illuminated by a 40 W incandescent light bulb serves as a source of bromine radicals. Various substituted toluenes (H, Me, tBu, Br, COOEt, COPh, NO 2) were brominated at the benzyl position. This haloperoxidase-like system for benzylic bromination does not require the presence of metal ions or an organic solvent for efficient conversion of methyl-arenes to benzyl bromides.
Debromination Reaction of 2-Bromocarboxylic Acids
Mendeleev Communications, 1994
Fax: + 7 095 135 5328 A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 1 17912 Moscow, Russian Federation. Fax: + 7 095 230 2224 2-Bromo-substituted carboxylic acids (RCHBrCOOH) undergo reductive debromination and form unsubstituted acids RCH,COOH.
Radical mediated-direct conversion of aldehydes into acid bromides
Tetrahedron Letters, 2007
A method of preparing acid bromides directly from aldehydes with Br 3 CCO 2 Et under radical conditions was developed. Aromatic aldehydes with electron-donating group were found to be more reactive than aromatic aldehydes with electron-withdrawing group and aliphatic aldehydes under reaction conditions.
Tetrahedron, 2009
A H 2 O 2-HBr system and N-bromosuccinimide in an aqueous medium were used as a 'green' approach to electrophilic and radical bromination. Several activated and less activated aromatic molecules, phenylsubstituted ketones and styrene were efficiently brominated 'on water' using both systems at ambient temperature and without an added metal or acid catalyst, whereas various non-activated toluenes were functionalized at the benzyl position in the presence of visible light as a radical activator. A comparison of reactivity and selectivity of both brominating systems reveals the H 2 O 2-HBr system to be more reactive than NBS for benzyl bromination and for the bromination of ketones, while for electrophilic aromatic substitution of methoxy-substituted tetralone it was higher for NBS. Also, higher yields of brominated aromatics were observed when using H 2 O 2-HBr 'on water'. Bromination of styrene reveals that not just the structure of the brominating reagent but the reaction conditions: amount of water, organic solvent, stirring rate and interface structure, play a key role in defining the outcome of bromination (dibromination vs bromohydroxylation). In addition, mild reaction conditions, a straightforward isolation procedure, inexpensive reagents and a lower environment impact make aqueous brominating methods a possible alternative to other reported brominating protocols.
Reduction of Bridgehead Halogens by an Intramolecular Electron Transfer Radical Mechanism
The Journal of Organic Chemistry, 1995
Reactions of 9,lO-dibromo-and 9,10-diiodo-2-nitro-9,10-ethano-9,10-dihydroanthracene (10 and 11, respectively) with the tertiary carbanions, 1,3,5, and 7-9, proceed exclusively by reduction at the bridgehead with no substitution products being observed. It is proposed that the reduction process occurs by a radical chain mechanism including an intramolecular electron transfer step and P-hydrogen abstraction from alkyl substituents on the participating carbanions. These ethanoanthracenes contain halogens at bridgehead positions that are meta-and para-benzylic relative to an aromatic nitro group, thus allowing the determination of the relative reactivities of the two benzylic sites within the same molecule. Quantitative studies on the reaction of 11 with sodium salts of 2-ethylmalononitrile and diethyl 2-ethylmalonate reveal that the reduction process is regioselective, with reduction occurring more readily at the benzylic bridgehead position para to the nitro group than at the corresponding meta-benzylic position. The ratio of meta:para reduction products, determined for the reaction of the diiodide 11 with several carbanions, was in the range 1:(1.6 f 0.2). This ratio contrasts with the differences in rate constants (approximately 2 orders of magnitude) determined for other nitrobenzylic systems, known to undergo S R N~ substitution reactions with the same nucleophiles. These differences in the ratio of rate constants of regioselective reduction compared with those observed for substitution reactions is discussed in terms of the C-X bond a t a bridgehead position lying orthogonal to the plane of the nitroaryl group. As a result of this geometry, the rate of intramolecular electron transfer is significantly reduced and the ratio of para-benzylic to meta-benzylic reactivity differs only by a factor of less than 2.
Radical Deoxyfunctionalisation Strategies
2022
Due to their abundance and readily available synthesis, alcohols provide ideal handles for the selective derivatisation of organic molecules. Radical chemistry offers versatile strategies for the conversion of Csp 3-O bonds into a wide range of Csp 3-C or Csp 3-heteroatom bonds. In these reactions, alcohols are readily derivatised with an activator group which can undergo facile mesolysis to generate a primary, secondary, or tertiary open-shell species that can engage in further transformations. These strategies are particularly effective at overcoming steric limitations associated with nucleophilic substitution pathways. Despite their potential, the use of radical deoxyfunctionalisation reactions as a general strategy for the synthesis of useful and complex molecules remains underutilised. Herein, we highlight recent advancements in this exciting field using photocatalysis, transition metal catalysis or electrochemistry to initiate the radical processes.
Aminoalkyl radicals as halogen-atom transfer agents for activation of alkyl and aryl halides
Science, 2020
Amines as a gateway to alkyl radicals In recent years, photoredox catalysis driven by blue light has often been used to oxidize carbon centers adjacent to nitrogen. Constantin et al. now show that these aminoalkyl radicals can, in turn, conveniently strip iodine atoms from a variety of alkyl carbons. The new alkyl radicals that result readily undergo deuteration and couplings such as alkylation, allylation, and olefination. The upshot is that simple amines can replace more hazardous conventional reagents such as trialkyltin compounds in the homolytic activation and functionalization of halocarbons. Science , this issue p. 1021
Dehydrobromination and debromination of 2,2, 7a-tribromocholest-4-en-3,6-dione
2012
Natural Product and Polymer Chemistry Laboratory, Department of Chemistry, University of North Bengal, Darjeeling-734 013, West Bengal, India E-mail : pizy12@yahoo.com Fax : 91-353-2699001 Manuscript received 21 February 201J, revised 31 May 2011, accepted 17 October 2011 The reaction of 2,2, 7<strong>α</strong>-tribromocholest-4-en-3,6-dione (1) with lithium bromide in <em>N,N</em>-dimethyl formamide furnished a single compound identified as 2-bromocholest-1,4-dien-3,6-dione (2) by spectroscopic methods <strong>(UV, FT-IR, NMR</strong> and <strong>Mas</strong>s).