Allyl halide

Allyl halides are a class of compounds in organic chemistry whose members contain a halogen atom in the allylic position, i.e., bonded to a carbon atom that is itself directly bonded to a double bond. In the narrower sense, they are monohalogenated derivatives of propene, namely allyl fluoride (Allyl fluoride), allyl chloride, allyl bromide, and allyl iodide.

Production

Selective bromination of alkenes in the allyl position is possible using Wohl-Ziegler bromination.[1] An alternative reagent is N-bromo-tert-butylamine.[2] Allylic chlorination of alkenes can be carried out with N-chlorosuccinimide and phenylselenyl chloride[3] or via a radical pathway with tert-butyl hypochlorite under irradiation[4] or, in the case of terminal alkenes, with cerium(III) chloride and sodium hypochlorite accompanied by rearrangement of the double bond. Allylic iodides can be prepared from allyl alcohols by reaction with sodium iodide / boron trifluoride etherate or with sodium iodide / trimethylsilyl chloride. Allyl fluorides can be prepared from allyl alcohols, with the most commonly used reagent by far being diethylaminosulfur trifluoride. Less frequently used alternatives include Yarovenko's reagent; N,N-Diisopropyl-1-fluoro-2-methylpropenamine; a reagent system consisting of iodine pentafluoride, hydrogen fluoride and triethylamine; or sulfur tetrafluoride. Substitution of chlorine or bromine atoms or tosyl groups with fluorine is also possible, for example using tetrabutylammonium fluoride or lead(II) fluoride. Allylic fluorination of alkenes can be achieved with electrophilic fluorinating agents, for example acetyl hypofluorite, N-fluoropyridinium triflate, various other N-fluorinated pyridinium compounds, as well as Accufluor and Selectfluor. Furthermore, allyl fluorides can be produced by forming a double bond, for example via the Horner-Wadsworth-Emmons reaction of α-fluorinated aldehydes and ketones. Finally, reduction of the corresponding propargyl group is also possible.[5]

One method for the preparation of primary allyl halides is the reaction of a ketone with vinyl magnesium bromide in tetrahydrofuran, followed by halogenation of the resulting allyl alcohol with a carboxylic acid halide (acetyl chloride or acetyl bromide) in dichloromethane.[6]

Reactions

Allyl halides can be converted into the corresponding organometallic compounds, which can be used to transform carbonyl compounds into homoallyl alcohols by allylation. This enables reactions such as the Barbier reaction or reactions involving low-valent chromium. In addition, allyl halides such as allyl chloride, allyl bromide and allyl iodide can be converted into Grignard reagents, which can likewise be used for the synthesis of homoallyl alcohols. The use of a catalytic amount of titanium dichloride suppresses Wurtz coupling as a side reaction.

Allylic iodides (generated in situ if necessary) are suitable for the generation of nucleophilic allylation reagents (reaction with zinc, reversal and subsequent Barbier-type reaction) or can be used directly as electrophilic allylation agents. They can be converted into allylic azides with sodium azide, into unsaturated nitriles with cyanides, or into sulphones.[7]

Allyl bromides can be converted into iodalkynes by homologization with sodium hexamethyldisilazide and iodoform.[8] Allyl fluorides can participate in many reactions typical of alkenes, including cycloaddition, formation of epoxides, dihydroxylation, ozonolysis, bromination or hydrogenation.[5]

Allyl halides can be used for the preparation of allyl metal complexes, for example of iron, nickel, cobalt, palladium and platinum.[9]

References

  1. ^ Bruckner, Reinhard (2010-01-20), Organic Mechanisms: Reactions, Stereochemistry and Synthesis, Springer Science & Business Media, ISBN 978-3-642-03650-7
  2. ^ Boozer, C. E.; Moncrief, J. W. (February 1962), "Allylic Bromination by N-Bromo-t-butylamine 1", The Journal of Organic Chemistry, vol. 27, no. 2, pp. 623–624, doi:10.1021/jo01049a502
  3. ^ Tunge, Jon A.; Mellegaard, Shelli R. (2004-04-01), "Selective Selenocatalytic Allylic Chlorination", Organic Letters, vol. 6, no. 8, pp. 1205–1207, doi:10.1021/ol036525o
  4. ^ Walling, Cheves; Thaler, Warren (September 1961), "Positive Halogen Compounds. III. Allylic Chlorination with t-Butyl Hypochlorite The Stereochemistry of Allylic Radicals 1", Journal of the American Chemical Society, vol. 83, no. 18, pp. 3877–3884, doi:10.1021/ja01479a033
  5. ^ a b Pacheco, M. Carmen; Purser, Sophie; Gouverneur, Véronique (2008-06-01), "The Chemistry of Propargylic and Allylic Fluorides", Chemical Reviews, vol. 108, no. 6, pp. 1943–1981, doi:10.1021/cr068410e, ISSN 0009-2665, retrieved 2026-01-08
  6. ^ Kishali, Nurhan; Polat, M. Fatih; Altundas, Ramazan; Kara, Yunus (January 2008), "A Novel One‐Pot Conversion of Allyl Alcohols into Primary Allyl Halides Mediated by Acetyl Halide", Helvetica Chimica Acta, vol. 91, no. 1, pp. 67–72, doi:10.1002/hlca.200890014
  7. ^ Kanai, Takaya; Kanagawa, Yoshinori; Ishii, Yasutaka (May 1990), "Hydrogen iodide strategy for one-pot preparation of allylic azides, nitriles, and phenyl sulfones from allylic alcohols", The Journal of Organic Chemistry, vol. 55, no. 10, pp. 3274–3277, doi:10.1021/jo00297a053
  8. ^ Pelletier, Guillaume; Lie, Sharon; Mousseau, James J.; Charette, André B. (2012-11-02), "One-Pot Synthesis of 1-Iodoalkynes and Trisubstituted Alkenes from Benzylic and Allylic Bromides", Organic Letters, vol. 14, no. 21, pp. 5464–5467, doi:10.1021/ol302544s
  9. ^ Rieke, Reuben D.; Kavaliunas, Arunas V.; Rhyne, Lee D.; Fraser, David J. J. (January 1979), "Preparation of .pi.-allyl metal complexes by direct reaction of highly reactive transition metal powders with allylic halides", Journal of the American Chemical Society, vol. 101, no. 1, pp. 246–248, doi:10.1021/ja00495a055

See also

  • All pages with titles beginning with Allyl
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