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 10min yielded the corresponding 2-thiouracil 5b in 73% yield, in addition to the disulfide derivative 7 as a minor product.