Reactions of ethyl 2-alkyl-3-oxobutanoate with thiourea and methylthiourea

Abstract

The reaction of ethyl 3-oxobutanoate with N-methylthiourea in alkoxide medium gives a mixture (1 : 20) of 1,6-dimethyl-2-thiouracil and 3,6-dimethyl-2-thiouracil: the latter isomer has been isolated from the mixture and the former isomer has been prepared by independent synthesis. Dissociation constants of ethyl 2-alkyl-3-oxobutanoates (alkyl = methyl, butyl, or isopropyl) have been measured in methanol. Reaction of these esters with thiourea and N-methylthiourea gives the corresponding alkyl derivatives of 6-methyl-2-thiouracil. Kinetics of these reactions have been measured in methoxide medium. Effects of the alkyl groups on the reaction rates have been investigated, and a reaction mechanism is suggested.