Synthesis of 4-iodopyrazole derivatives

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2008
Yazıcı, Ceyda
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.

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Citation Formats
C. Yazıcı, “Synthesis of 4-iodopyrazole derivatives,” M.S. - Master of Science, Middle East Technical University, 2008.