Pyrazoles have been studied for over a century as an important class of
heterocyclic compounds and continue to attract considerable interest due to the
broad range of biological activities they possess. The electrophilic cyclization of
the acetylenic hydrazones initiated by molecular iodine could provide new ways of
synthesizing biologically active 4-iodopyrazole derivatives, which are important
precursors for the synthesis of highly substituted pyrazole derivatives. For this
reason, we investigated the synthesis of 4-iodopyrazole derivatives, such as 1-aryl-
5-alkyl/aryl-4-iodopyrazoles, starting from phenylhydrazine and ,-acetylenic
aldehyde derivatives. Initially, ,-acetylenic aldehydes were synthesized by
formylation reaction of corresponding alkynes with DMF. Then, hydrazone
derivatives of these aldehydes were prepared by heating them with
phenylhydrazine in a neat manner at 55 ° / C for 5 h. Finally, acetylenic phenyl
hydrazone derivatives were subjected to electrophilic cyclization by treating with
excess molecular iodine at 80 ° / C for 3 h. Although electrophilic cyclization is
commonly used in organic chemistry, it has not been employed for the cyclization
of acetylenic phenyl hydrazones to pyrazole derivatives. Under optimized
conditions, these reactions afforded 1-aryl-5-alkyl/aryl-4-iodopyrazole derivatives in moderate to good yields as the single or the major product of the reactions. In
some cases, 1-aryl-5-alkyl/arylpyrazole derivatives resulted from these reactions as
minor products. In conclusion, 4-iodopyrazole derivatives were synthesized for the
first time directly from acyclic starting materials, ,-acetylenic phenylhydrazones
and iodine, via electrophilic cyclization.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/3/12609750/index.pdf |
| Date | 01 August 2008 |
| Creators | Yazici, Ceyda |
| Contributors | Zora, Metin |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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