Facile a-Halogenations of cyclic enones and linear enals.
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2007
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eng
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Mahidol University
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Pakorn Bovonsombat, Rungkarn Rujiwarangkul, Thanathip Bowornkiengkai, Juthamard Leykajarakul (2007). Facile a-Halogenations of cyclic enones and linear enals.. Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/32894
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Facile a-Halogenations of cyclic enones and linear enals.
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A facile methodology for the formations of α -chloro, α -bromo and α -iodo cyclic enones and
linear enals has been developed. In our method, a combination of pyridine or pyridine-Noxide,
and various N-halosuccinimides are employed to convert enones or enals in various
solvents at room temperature to α -haloenones or α -haloenals.
Previously, α -iodination of enones, both cyclic and linear, could be affected by small
amounts of pyridine and stoichiometric iodine.(1) α -Iodination of several cyclic and linear
enones were also reported to be effective with combination of iodine and excess quantities of
pyridine using carbon tetrachloride as co-solvent.(2)Other reagents for α -iodination of enones
include morpholine,(3) and pyridinium dichromate (PDC) and iodine.(4) With linear enones, the
combination of pyridine and I2 required refluxing acetonitrile to obtain a maximum 62%
yield for (Z)-4-iodo-4-hexen-3-one.1 With PDC and iodine, (E)-4-hexen-3-one reacted to
yield less than 5% conversion to its α -iodo analogue.4 Extending the reactions to linear
enones and to α -bromination and α -chlorination are limited due to low yields and uses of
toxic bromine and chlorine. Previous methods for α -chlorination include hydrochloric acid
and m-chlorobenzoic acid.(5) Reagents for α -bromination are iodobenzene diacetate with
tetrabutylammonium bromide,(6) and Rhodium (III) complex combined with acid halides or
benzyl halides.(7) In our general methodology for α -halogenation of both cyclic enones and linear enals, α -
halogenations proceeded facilely with good to excellent yields and with retention of geometry
across the double bond for the linear enals and also with retention of the sensitive aldehyde
group.
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Thailand Research Expo 2007, September 7-11, 2007, Bangkok, Thailand