Facile a-Halogenations of cyclic enones and linear enals.
6
Issued Date
2007
Resource Type
Language
eng
Rights
Mahidol University
Suggested Citation
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
Title
Facile a-Halogenations of cyclic enones and linear enals.
Other Contributor(s)
Abstract
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.
Description
Thailand Research Expo 2007, September 7-11, 2007, Bangkok, Thailand