Suzanne Gelin

4-Oxo-1H-and-2H-[1]benzopyrano[4,3-c]pyrazoles. Preparation from 4-hydroxycoumarin or 3-chromonecarboxylic acid derivatives.

Abstract The conversion of 3-acyl-4-hydroxycoumarins to either 4-oxo-1-phenyl-1H-[1]benzopyrano[4,3-c]pyrazoles 2 or 4-oxo-2-phenyl-2H-[1]benzopyrano[4,3-c]pyrazoles 3 is described. The product obtained from the reaction of phenylhydrazine with 3-chromonecarboxylic acid 6a has been established not to be such 2-phenyl[1]benzopyrano[4,3-c]pyrazol-3-2H-one 7 as previously reported but to be 4-oxo-1-phenyl-1H[1]benzopyrano[4,3-c]pyrazole 2a . Our results showed evidence that the method precedently described as yielding 2a , from 4-chloro-3-formyl-coumarin was an implausible one.

Tetronic acids and derivatives-IV: Synthesis and lactonization of -γ-acetoxy β-ketoesters

Abstract Through our investigation of synthetic routes to tetronic acids, elaboration and cyclization of γ-acetoxy-β-ketoesters were examined. Synthesis of these β-ketoesters 2 has been realized by selective monoacylation of the magnesioenolate of monoethyl malonate. Lactonization of 2 leading to tetronic acids or to 4-alkoxy-furan-2(5 H )-ones is reported.

Tautomerism in acyl tetronic acids

Abstract The tautomeric structures of some acetyl tetronic acids are studied by NMR analysis.

Synthesis of 4-oxo-1,4-dihydro-6h-furo[3,4-c]pyrazole and 4-oxo-1,4,5,6-tetrahydropyrrolo[3,4-C]pyrazole Systems from Acyl Tetronic and Tetramic Acids

Abstract The reaction of acetyl tetronic acid la with phenylhydrazine had been reported to lead to 3-(1-phenylhydrazonoethyl)-tetronic acid 3, which by ring closure afforded the pyrazole-lactone 5a1. On the other hand, condensation of acetyl tetramic acids 2a,b with phenylhydrazine and methylhydrazine had been described as yielding 4-oxo-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole derivatives 9 via the hydrazones 4 2. The lack of reactivity of the carbonyl of the acetyl side chain towards hydrazines is amazing in view of the affinity shown by this group for reactions with amines 3–5. We therefore reinvestigated these structures and we now wish to present evidence for the formation of 1-substituted-4-oxo-1,4-dihydro-6H-furo[3,4-c]pyrazoles 5 and 6 and 1-substituted-4-oxo-1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles 7 and 8 and not 2,4,5,6-tetrahydropyrazoles 9 as previously described 2.

Tetronic acids and derivatives—VII: Structure of dehydroascorbic acid osazone and related compounds

Abstract 13 CNMR spectral examination of ascorbic acid and tetronic acid osazones favours a bis(phenylhydrazono) formula and not, as recently reported, a phenylhydrazino-phenylazo structure. Similar conclusions were reached for related 5H -furan-2-ones 2-4 bearing at the C-3 and C-4 positions an oximino or an oximino and a phenylhydrazono group. Based on 1 H NMR , IR and UV data, the mutarotation in solution and the chelated structures of compounds 1-4 are discussed.

Tetronic Acids and Derivatives Part VIII (1) o-Alkylation of 3-Unsubstituted Tetronic Acids

Abstract 4-methoxy-(5H)-furan-2-ones 1 are useful starting materials for the synthesis of naturally occuring lactones2. In a previous communication we have described an efficient entry to 4-alkoxy-(5H)-furan-2-ones 1–3 (alkyl tetronates) by lactonization of ethyl 4-acetoxy 3-ketoesters 4 using hydrochloric acid in several alcohols1. The detection of 4-hydroxy-(5H)-furan-2-ones 5 (tetronic acids) during the reaction course3 allowed us to postulate them as intermediates which were subsequently etherified to the products 1–3. In a very recent communication4, it was claimed that attempted alkylation of tetronic acids 5 using HC1 in an alcohol or alkyl halides on tetronic acids sodium salts are unsuccessful; moreover, the structure of our compounds 1–3 was questionned by arguing that isomeric 2-alkylated materials

A new ring transformation: Synthesis of 5,5-dimethyl-3-oxo-1-pyrroline 1-oxides from 6,6-dimethyl-4-oxo-5,6-dihydro-1,2,4h-oxazines

Abstract The nitrosation of some γ,δ-unsaturated β-diketo compounds affords the 3-substituted 4-oxo-5,6-dihydro-1,2,4H-oxazines. These compounds are converted to the isomeric 3-oxo-1-pyrroline 1-oxides by a facile thermal rearrangement.

Tautomerism in 3-nitrotetronic acids

Abstract The controversial structure of the title compounds has been established. The previously reported strong intramolecular hydrogen bond was found to be absent.

Photocyclization of 5-(1-alkenyl)-1-phenylpyrazoles : a convenient synthesis of 4,5-dihydropyrazolo[1,5-gaquinolines

Abstract The photocyclization of some 5-(1-alkenyl)-4-ethoxycarbonyl-1-phenylpyrazoles affords 3-ethoxycarbonyl-4,5-dihydropyrazolo[1,5- a ]quinolines which are decarboxylated to the 3-unsubstituted analogs.