Some Observations on the Base-Catalyzed Cyclocondensation of 2,6-Dihalobenzaldehydes, Ethyl Cyanoacetate, and Thiourea

Abstract

The reaction of 2,6-difluorobenzaldehyde, 2-chloro-6-fluorobenzaldehyde, or 2,6-dichlorobenzaldehyde and ethyl cyanoacetate and thiourea, in the presence of potassium carbonate, yielded a mixture of the cis- and trans-5,6-dihydro-2-thiouracil derivatives 4a–c. Compounds 4a–c, which were found to be resistant to atmospheric oxidation even at high temperatures, were successfully dehydrogenated to 5a–c via prolonged heating with chloranil in toluene. Meanwhile, oxidation of the dihydro derivative 4b by heating in dimethylsufphoxide for 10 min yielded the corresponding 2-thiouracil 5b in 73% yield, in addition to the disulfide derivative 7 as a minor product.

Keywords:

• Antimicrobial activity
• cyclocondensation
• 5,6-dihydro-2-thiouracils
• 2-thiouracils

ACKNOWLEDGMENTS

The financial support of the Research Center of the College of Pharmacy, King Saud University (Project C.P.R.C. 174), is greatly appreciated. The authors are greatly indebted to Dr. Elsayed E. Habib, Department of Microbiology, University of Mansoura, Egypt, for performing the antimicrobial screening.