Enaminones are versatile reagents and their chemistry has recently received considerable interest. 1 Having multiple electrophilic and nucleophilic centers, enaminones react with both electrophiles and nucleophiles. [1][2][3] Moreover, enaminones also undergo a variety of cycloaddition and self condensation reactions. 1,4,5 In previous work from our laboratories we have explored the chemistry of enaminones with aryl moieties. [4][5][6][7][8][9][10][11] In conjunction with this work and because of recent interest in enaminone chemistry we report here the synthesis of two enaminone derivatives with acyl moiety, and a study of their chemical behaviour, which was found to differ in some respects from previously reported behaviour. Moreover, where possible we present a comparison of the results of conventional and microwave heating. The utility of microwave heating in synthesis is now well recognised "green technology". 12,13 Results and discussionHeating DMFDMA with an excess of 2-butanone (1a) (R = Et) under reflux for 24 hours, then subsequent evaporation of excess of 2-butanone, afforded a yellow oily product of molecular formula C 7 H 13 NO. The 1 H NMR spectrum established the structure as (E)-1-N,N-dimethylaminopent-1en-3-one 2a, and ruled out the (Z)-isomer 3a, since it showed two olefinic proton signals at δ 5.85 and 7.5 ppm with J = 16 Hz which is a typical value for trans coupled protons in 1,2disubstituted olefins (Scheme 1).Similarly, 1-(4-acetylphenyl)ethanone (1,4-diacetylbenzene) (1b) condensed with DMFDMA to yield a product for which the trans structure 2b was assigned based on 1 H NMR which revealed two trans coupled olefinic protons (δ 5.9, 7.3 ppm, J = 14 Hz, for H-2 and H-3 respectively). The formation of 1-(4-acetylphenyl)-3-(dimethylamino)propenone 2b using the literature 3 procedure required reflux for 6 hours and went in 65% yield, while microwave irradiation dramatically reduced the reaction time to 3 minutes with an improvement in the isolated yield (96%) (cf. Table 1). Condensation of 1b with two moles of DMFDMA in dry toluene yielded the 3-dimethylamino-1-[4-(3-dimethylaminoacryloyl)phenyl] propenone 4.Compound 2a,b reacted with 1,4-naphthoquinone to yield products of addition and dimethylamine elimination. These can be assigned structures 6, formed through the intermediate Michael adducts 5. The 1 H NMR of the reaction products revealed the presence of formyl signals, at δ 9.1 ppm (6a), 8.7 ppm (6b). Thus structures 6a,b were assigned to the reaction products. Similar to its behaviour toward 1,4-naphthoquinone, compound 2a also reacted with 1,4-benzoquinone to yield 7 (δ CHO 8.9 ppm). (Scheme 1) Similar to reported behaviour of enaminones, compound 2a, coupled with aromatic diazonium chloride in the presence of ethanolic sodium acetate to yield the corresponding coupling product that are assumed to exist as an equilibrium mixture of the hydrazone structures 8 and 9 rather than the azo-enol structures 10 or 11, based on the 1 H NMR spectrum. The 1 H NMR revealed that, at least in DMSO sol...

A novel synthesis of arylpyrazole, isoxazole, dialkyl 1,6-dihydropyridazine 5,6-dicarboxylate derivatives and a new one-step synthesis of azolopyrimidines under microwave-assisted conditions are reported.

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To cite this article: Abdellatif Salah El-Din (2003) Fused thiazole from 2-(4-phenyl-3(h)-thiazol-2-ylidene) malononitrile: A novel synthesis of thiazolo[3,2-c ]pyrimidine, thiazolo[3,2-a ]pyridine, pyrazolo[3,4-d ]-1,3-thiazolino[2,3-f ]pyrimidine and arylazo thiazolylidene derivatives, Sulfur Letters, 26:1, 35-41, 2-(4-Phenyl-3(H)-thiazol-2-ylidene) malononitrile was obtained from cyclo-condensation of cyanatoacetophenone with malononitrile and not via the Knoevenagel condensation, depending on the reaction conditions. The synthesis of thiazolo[3,2-a]pyridine, thiazolo[3,2-c]pyrimidine, pyrazolo[3,4-d]-1,3-thiazolino[2,3-f]pyrimidine and some azo derivatives of thiazolidene are described.