Fused pyrimidine derivatives R 0515Chemoselective Cyclocondensation of α-Acylacetamidines with 2-Methylsulfanyl-4,6-dichloropyrimidine-5-carbaldehyde. -(RYAZANOV, S. G.; SELIVANOV, S. I.; DAR'IN, D. V.; LOBANOV, P. S.; POTEKHIN, A. A.; Russ. J. Org. Chem. 44 (2008) 2, 288-291; St. Petersburg State Univ., St. Petersburg 198904, Russia; Eng.) -A. Forchert 01-169

The cyclocondensation of α-acylacetamidines with esters of 2-fluoro-5-nitrobenzoic and 4-chloro-2-methyl-5-pyrimidinecarboxylic acids leads to condensed azines. The reaction proceeds chemoselectively such that the α-carbon atom of the amidine replaces the halogen atom in the aromatic ring, while the amino group reacts with the ester group.In a continuation of our study of the reactivity of α-acylacetamidines with aromatic dielectrophiles [1, 2], we investigated the reactions of amidines 1a-c with esters 2 and 4. α-Acylacetamidines 1a-c exist in DMSO-d 6 solution in the enediamine tautomeric form, which accounts for their C,N-dinucleophilic properties upon reaction with dielectrophiles.α-Acylacetamidines 1a-c act as C,N-dinucleophiles in their reactions with ester 2 and selectively give the corresponding isoquinolines 3 in good yield. The reactions with amidines 1a and 1b were carried out at room temperature. The reaction with benzoylacetamidine 1c proceeds more slowly and required heating to 50°C.We should note that our proposed method for the synthesis of isoquinolines 3 complements a recently reported method for the synthesis of analogous 3-aminoisoquinolines from amides of 2-chloro-5-nitrobenzoic acid and aryl and hetaryl acetonitriles [3,4].The reaction of amidines 1a and 1b with ester 4 proceeds smoothly at room temperature over 60-100 h and pyrido[4,3-d]pyrimidines 5a and 5b are formed in high yield. The reaction with amidine 1c proved rather slow as in the case of ester 2 but significant tar formation occurred upon attempting to carry out this reaction with heating. On the other hand, carrying out this reaction at room temperature required 60 days. The major product was also pyrido[4,3-d]pyrimidine 6c, which was isolated chromatographically as a mixture of E-and Zisomers as indicated by the double set of signals in the 1 H and 13 C NMR spectra.

The reaction of benzamidines with 2-bromo-and 2-iodobenzaldehydes catalyzed by the CuI/L-proline system has been studied. Reaction with 2-iodobenzaldehyde leads to the formation of quinazolines in good yield. 2-Bromobenzaldehyde forms 2-arylquinazolines in low yield due to the competing reaction involving two molecules of amidine leading to a dihydrotriazine.Keywords: benzamidine, 2-iodobenzaldehyde, quinazoline, catalysis by copper(I).Up to the present many efficient methods have been developed for the N-arylation of various nitrogen nucleophiles with aryl bromides and iodides using the Cu(I)/ligand system as catalyst [1][2][3][4][5][6][7][8][9][10][11]. Intramolecular reactions of such type lead to benzo-condensed heterocycles [12][13][14][15], which broaden significantly the possibility of synthesizing many difficultly available compounds of this family. These methods are attractive from the availability and cheapness of reactants, simplicity of use, and frequent high yields.The aim of the present work was the involvement of benzamidines in cyclocondensation with o-halobenzaldehydes in the presence of a catalyst (CuI) and the development based on it of a new method of synthesis of 4-unsubstituted quinazolines, which are usually obtained in several stages and not always in good yield [16,17]. There was no information in the literature at the beginning of our investigation on such reactions. However, in the course of our work a report appeared from Chinese authors [18], which described the interaction of amidines with various aromatic aldehydes, ketones, and esters containing an atom of chlorine or bromine in the ortho position. In particular, 2-bromobenzaldehyde gives 2-substituted quinazolines in yields of 55-82% with amidines on catalysis with the CuI/L-proline system.In our experiments the reaction of 2-bromobenzaldehyde with amidines proceeded esentially by other route. We tested various conditions. The temperature regime, reaction time, solvent, and base were varied. The most characteristic experiments are given in Table 1. The yield of 2-phenylquinazoline 3a in the reaction with benzamidine did not exceed 32%. On carrying out the reaction with other ligands (N,N'-dimethylethylenediamine, ethylene glycol, 8-hydroxyquinoline) the target compound was formed in only trace amounts or was not formed at all. Variation of the reactant/catalyst ratio and the use of 4 Å molecular sieve did not affect the yield of quinazoline. Precise reproduction of the conditions of [18] also did not lead to the formation of quinazoline in satisfactory yield.

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