Some Observations on the Base-Catalyzed Cyclocondensation of 2,6-Dihalobenzaldehydes, Ethyl Cyanoacetate, and Thiourea
作者:Mohamed A. Al-Omar、Abdul-Rahman M. Al-Obaid、Nasser R. El-Brollosy、Ali A. El-Emam
DOI:10.1080/00397910903098730
日期:2010.4.26
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 10min yielded the corresponding 2-thiouracil 5b in 73% yield, in addition to the disulfide derivative 7 as a minor product.