“…1327 The bromofluorination reaction was further developed by Chehidi et al using NBS and triethylamine tris(hydrofluoride). 1328 They found that the treatment of allylic alcohols using a combination of NBS and Et 3 N•3HF produces vicinal fluorobromohydrins in high yield. Mekini et al extended this procedure for the bromofluorination of bis(allyl)poly(oxyethylene) glycol ethers.…”
Section: Cohalogenation Reaction With Nbsmentioning
confidence: 99%
“…However, the bromofluorination of allyl benzene under the same conditions resulted in the formation of both Markovnikov and anti-Markovnikov products in a 7:1 ratio . The bromofluorination reaction was further developed by Chehidi et al using NBS and triethylamine tris(hydrofluoride) . They found that the treatment of allylic alcohols using a combination of NBS and Et 3 N·3HF produces vicinal fluorobromohydrins in high yield.…”
Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.
“…1327 The bromofluorination reaction was further developed by Chehidi et al using NBS and triethylamine tris(hydrofluoride). 1328 They found that the treatment of allylic alcohols using a combination of NBS and Et 3 N•3HF produces vicinal fluorobromohydrins in high yield. Mekini et al extended this procedure for the bromofluorination of bis(allyl)poly(oxyethylene) glycol ethers.…”
Section: Cohalogenation Reaction With Nbsmentioning
confidence: 99%
“…However, the bromofluorination of allyl benzene under the same conditions resulted in the formation of both Markovnikov and anti-Markovnikov products in a 7:1 ratio . The bromofluorination reaction was further developed by Chehidi et al using NBS and triethylamine tris(hydrofluoride) . They found that the treatment of allylic alcohols using a combination of NBS and Et 3 N·3HF produces vicinal fluorobromohydrins in high yield.…”
Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.
“…Regioselective and stereospecific ring opening of 2 with BF 3 yielded (2 S ,3 R )-3-fluoro-2-hydroxy-3-phenylpropyl p -toluenesulfonate ( 3 ), which was converted into 1 in essentially quantitative yield by intramolecular nucleophilic displacement induced by lithium tert -butoxide (Scheme ). This procedure allows for the preparation of enantiopure 1 on a multigram scale without any difficulty. , To our knowledge, 1 is the first chiral derivatizing agent introduced through the ring-opening of an epoxide that has been successfully tested. 1 Preparation of Resolution Reagent 1 from (2 S, 3 S )-Phenylglycidyl p -Toluenesulfonate ( 2 ) …”
(S)-2-[(R)-Fluoro(phenyl)methyl]oxirane is a new, synthetic, yet enantiopure, chiral resolution reagent, readily obtained from enantiopure (2S,3S)-phenylglycidol, that reacts with a variety of alpha-chiral primary and secondary amines in a straightforward manner through a regioselective ring-opening. Diastereomeric products are easily identified and quantified by (19)F, (1)H, and (13)C NMR and by HPLC, which makes this fluorinated compound a most versatile reagent for the analysis of scalemic mixtures of amines. [reaction: see text]
“…Attempts to prepare 3-bromo-2-fluoropropene (4) by bromofluorination of allylic bromide followed by dehydrobromination have been thwarted by lack of regioselectivity in the addition step. 10,11 However, we found that 3bromo-2-fluoropropene (4) could be efficiently obtained in three steps via 2-fluoroallylic alcohol 3 starting with ammonium α -fluoroacrylate (1) 12 (Scheme 1 ) . The direct reduction of 1 with LiAlH 4 could not be accomplished.…”
3-Bromo-2-fluoropropene (4) is prepared in a new three-step synthesis from ammonium α -fluoroacrylate (1) in 31% overall yield. Glycine and alanine ester imines are efficiently alkylated by 4 to give, after deprotection, 2-amino-4-fluoropent-4-enoic acid (9) in 63% overall yield, and the α -methylated derivative 13 in 26% overall yield, respectively. Preliminary results indicate that 4 is potentially a new α -carbonyl cation equivalent. Key words: alkylation, amino acid ester imines, β -fluoroallyl bromide, 2-amino-4-fluoropent-4-enoic acid, α -carbonyl cation equivalentThe interest in partially fluorinated organic compounds has grown continuously over the last few years. 1 Nevertheless, the synthesis of highly functionalized molecules containing a limited number of fluorine atoms still remains a significant challenge to synthetic organic chemists.Recently, we reported the syntheses of racemic 2 and optically active 3 γ -and δ -fluoro-α -amino acids using easily accessible fluorinated building blocks. Glycine ester imines have been alkylated with 1-bromo-2-fluoroalkanes 4 in good yields, in spite of the deactivating influence of the fluorine substituent in β -position to the reaction center. 5 We then became interested in the application of 3-bromo-2 -fluoropropene (4) , which should be a more reactive alkylating reagent compared to the saturated β -fluorinated alkyl bromides.Until now β -fluoroallylic compounds have been infrequently used as building blocks. Only a few C-C bond formation reactions of these compounds have been described in the literature. 6 For example, one such compound has been used for the alkylation of Schöllkopf's bislactim ether. 6, 7 However, they have been already shown to participate well in substitution reactions with non-carbon nucleophiles 6 and esters of β -fluoroallylic alcohols have also been used for hetero-Cope rearrangements. 8 3-Bromo-2-fluoropropene (4) , previously prepared in a three-step synthesis from methyl vinyl ether in low overall yield, has been used for O -alkylation by Schlosser et al. 9 We report here a more efficient preparation of 4 and its use for C -alkylation of amino acid ester imines.Attempts to prepare 3-bromo-2-fluoropropene (4) by bromofluorination of allylic bromide followed by dehydrobromination have been thwarted by lack of regioselectivity in the addition step. 10, 11 However, we found that 3-bromo-2-fluoropropene (4) could be efficiently obtained in three steps via 2-fluoroallylic alcohol 3 starting with ammonium α -fluoroacrylate (1) 12 (Scheme 1 ) . The direct reduction of 1 with LiAlH 4 could not be accomplished. However, compound 3 could be synthesized by treatment of 1 with SOCl 2 , followed by reduction of the α -fluoroacrylic acid chloride with LiAlH 4 in diethyl ether at -20 ˚C. Although the reduction step was nearly quantitative, the overall yield of 3 was only 37% in this sequence. The most convenient synthesis of 3 involved the reduction of the benzyl ester 2 with LiAlH 4 in diethyl ether. The ester 2 was prepared under mild conditions by ...
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