3-Ethoxy-2-methoxymethylenepropionitrile (I) or its acetal (II) undergo condensation with urea, N-sub-stituted ureas, thiourea, and N-substituted thiourea. The condensation has been carried out by heating the enol ether propionitrile (I) or acetal propionitrile (II) in ethanol solution, in the presence of hydrochloric acid, with urea to obtain directly 5-cyano-2-oxo-l,2,3,4-tetrahydropyrimidine (III), with , '-dimethylurea to yield 5-cyano-l,3-dimethyl-2-oxo-l,2,3,4-tetrahydropyrimidine (IX), with N-methylurea to give a mixture of 5cyano-l-methyl-2-oxo-l,2,3,4-tetrahydropyrimidine (X) and its isomeric 3-methyl compound (XI), which was separated into each isomer, and with N-phenylurea to obtain exclusively the 1-phenyl compound (XV). Further dehydrogenation of these compounds made possible a new synthetic route to pyrimidines. The condensation was also carried out with thiourea and I or II in alcoholic solution in the presence of hydrochloric acid to obtain 5-cyano-2-oxo-6H-2,3-dihydro-l,3-thiazine (XVIII) and with N-phenylthiourea to give XVIII and aniline.Elucidation of the structures of these compounds is described.We have previously reported the reaction of acetami-dine3 and related amidines4 with 3-ethoxy-2-methoxymethylenepropionitrile (I) to give 2-substituted 4amino-5-ethoxymethylpyrimidines, and with 3-ethoxy-2-ethoxymethoxymethylpropionitrile (II) to yield 2,7disubstituted 5,6-dihydropyrimido [4,5-d Ipyrimidines.3 4 This paper deals with the reaction of I or II with urea, N-substituted ureas, thiourea, and N-substituted thiourea (see Scheme I).Reaction of I, a mixture of geometrical isomers,6with urea was carried out in ethanol solution in the presence of hydrochloric acid. The base-catalyzed condensation of aldehyde nitrile derivatives with urea is a standard synthesis of cytosine derivatives.6 However, in this case a product III, C5H5N3O, was obtained in 42.6% yield by acid-catalyzed reaction, and no evidence for the formation of other products was shown by thinlayer chromatography of the filtrate. The infrared spectrum of III shows NH bands, a conjugated C=N band, and an amide I band. Hydrolysis of III in concentrated hydrochloric acid gave the amide IV. Acetylation with acetic anhydride afforded the diacetate V. The proton magnetic resonance spectrum7 of V (Table I) shows two singlet signals (3H) at r 7.32 and 7.40 arising from the protons of 1-and 3-N-acetyl groups, respectively. The signals of the protons of C-4 methylene and C-6 methylidyne groups appear at r 5.56 (2H) and 2.05 (1H), respectively; the former is
