This communication reports on the investigation of a new recyclization conversion of a pyrimidine ring, which can be referred to as C-C recyclization. In this reaction the nucleophile cleaves the pyrimidine ring at the N(3)-C(4) bond, and following rotation around the single C(5)-C(6) bond the new cyclization takes place. This type of recyclization has general applicability, and takes place upon alkali treatment of substituted 4-methyl-5-ethoxycarbonyl-and 4-amino-5-ethoxycarbonylpyrimidines (1) which are transformed respectively to 4-hydroxy-5-acetyl-and 4-hydroxy-5-carbamoylpyrimidines (2). The obtained pyrimidyl-ketones can be readily converted to their hydrazones 7-12.

Recyclization of pyrimidines occurring with substitution of the endocyclic carbon atom C (4) by a nonring carbon atom of the 5-ethoxycarbonyl group was reported earlier in [1,2]. Such a rearrangement was classified as C-C recyclization of pyrimidines, in contrast to N-N recyclization (the Dimroth rearrangement) [3] and N-C recyclization (the Kost-Sagitullin rearrangement) [4].In studying the condensation of hydrochlorides of acetamidine (1a) and phenylacetamidine (1b) with ethoxymethylene acetoacetate in the presence of sodium ethoxide, we noted that the amount of sodium ethoxide has a considerable effect on the direction of heterocyclization. We found that for an equimolar ratio of the amidines, ethoxymethylene acetoacetate, and sodium ethoxide, we obtain 5-ethoxycarbonyl-2-methyl(2-benzyl)-4-methyl-pyrimidines 2a,b in high yield; while for a two-fold excess of sodium ethoxide relative to the amounts of the reagents used, 5-acetyl-4-hydroxy-2-methyl(2-benzyl)pyrimidines 3a,b are formed.We hypothesize that in the case of an excess of sodium ethoxide, as for an equimolar ratio of the reagents, the reaction initially occurs with formation of compounds 2. However, during treatment, the base formed in the presence of water (for excess sodium ethoxide) leads to recyclization of compounds 2 to form pyrimidines 3. N N Me R COOEt N N R COMe OH R NH NH 2 Me CHOEt O COOEt KOH EtONa HCl . 2a,b 3a,b 1a,b 1:1:1 1:2:1 1-3 a R = Me, b R = Bn.

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Among recyclizations of pyrimidines the most studied are Dimroth rearrangements [1] accompanied by exchange of a ring heteroatom with an exocyclic nitrogen atom (N-N recyclization conditions). We have studied a schematic relative of the Dimroth rearrangement in detail for conversion of pyrimidines to pyridine derivatives (the Kost-Sagitullin rearrangement [2][3][4][5][6]). Under these conditions a nitrogen atom of the pyrimidine ring is substituted by an exocyclic carbon atom occurring at the 2 position (N-C recyclization conditions). This communication relates to our study of a further recyclization conversion of pyrimidines which, according to the evidence, involves the substitution of an atom in the heterocycle and is a C-C recyclization. A similar rearrangement has previously been noted in a series of 2-substituted 5-carbethoxy-4-methylpyrimidines. Upon heating in sodium ethylate solution they are converted to the corresponding 2-substituted 5-acetyl-4-hydroxypyrimidines [7]. We have previously shown [8] that 2-substituted 4-amino-5-carbethoxypyrimidines are converted to the corresponding 5-carbamoyl-5-hydroxypyrimidines by treatment with base. It is also clear that the transformation noted above for the 5-carbethoxy-4-methylpyrimidines is, in fact, only achieved when treating the reaction mixture with water, i.e. under the action of hydroxide ion formed in solution.In a continuation of this work we have studied the possibility of carrying out similar rearrangements for condensed bicyclic pyrimidines, in particular for 6-carbethoxy-7-methylpyrazolo[1,5-a]-and 6-carbethoxy-7-methyl-1,2,4-triazolo[1,5-a]pyrimidine derivatives. Model compounds for study were synthesized by condensation of ethyl ethoxymethyleneacetoacetate in ethanol with systems containing amidine fragments, viz. 3-aminopyrazoles and 3-amino-1,2,4-triazole.__________________________________________________________________________________________