Durch Bromierung ausgelöste Umlagerung tertiärer Allylalkohole: Der Einfluss eines Fluor‐Substituenten auf Reaktionsgeschwindigkeit und Reaktionsverlauf

Nagakura, Isao; Savary, D. N.-H.; Schlosser, Manfred

doi:10.1002/hlca.19800630517

Cited by 10 publications

(3 citation statements)

References 19 publications

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“…Our retrosynthetic approach to 2 was based on 2-fluoroallylic alcohol ( 3 ) as a starting material (Scheme ). Surprisingly, although the compound 3 has already been described in the literature, we found no efficient and straightforward method for its practical preparation from commercially available materials. Therefore, a procedure to obtain 3 directly from commercially available methyl 2-fluoroacrylate ( 4 ) was elaborated (Scheme ).…”

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confidence: 80%

4-Fluoro-2,4-methanoproline

et al. 2009

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confidence: 80%

4-Fluoro-2,4-methanoproline

et al. 2009

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“…The 1 H, 19 F NMR and MS data agree with published values. 20 13 C NMR: δ = 60.3 (dt, 2 J C,F = 33.1 Hz, CH 2 OH), 90.9 (dt, 2 J H,F = 15.3 Hz, =CH 2 ), 164.5 (ds, 1 J C,F = 260.0 Hz, CF). IR (film): ν = 3381 (s, O-H), 1684 cm -1 (s, C=C).…”

Section: -Fluoroprop-2-en-1-ol (3)mentioning

confidence: 99%

3-Bromo-2-fluoropropene - A Fluorinated Building Block. 2-Fluoroallylation of Glycine and Alanine Ester Imines

Laue¹,

Haufe²

1998

Synthesis

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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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“…This regioselectivity is attributed to exclusive initial migration of the most-substituted carbon as the partial carbocation character in the transition state is stabilized by inductive effects and hyperconjugation. 51 52 The migratory ability of carbon moieties in such migratory shifts has been well-studied and not only explains the observed regioselectivity, but also the retention of stereochemistry at the migrating center. A further 1,2-sigmatropic rearrangement—supported by the acylium-like character of the carbonyl group—affords the trans -1,2-dimethylated 4-tetralone after aromatization, intercepting Nishida’s route towards carbazomycins A and B in very short order (three vs eight synthetic steps in the longest linear sequence from indole).…”

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confidence: 99%