Mirella Scotton

Synthesis of furo-furans by rearrangement of 4-acetylpyrans

Abstract The hetero-Diels-Alder reaction of 1-oxabutadienes 1a–c bearing electron-withdrawing groups with ethyl vinyl ether and 2,3-dihydrofuran gave the functionalized 5,6-dihydro-4H-pyrans 2a-c, 4c and 4H-4a, 5, 6, 6a-tetrahydrofuro[2,3-b]pyrans 5a-c and 6c. Cycloadducts 2a and 4c easily rearranged to furo[2,3-b]furans 3a, 3c and 9c and cycloadducts 5a and 6c to difuro[2,3-b:3′,4′-d]furans 7a, 7c and 8c. The stereochemistry of compounds 5c and 7a was determined by single crystal X-ray analysis. Relative configurations of the other compounds were established by nOe data. Some aspects of the reaction mechanisms are discussed.

Spiro-dihydrofuran-pyrazolidinones from tetraacetylethylene andazo-dicarbonyl compounds

Abstract Tetraacetylethylene (1) reacted with electron-withdrawing azo compounds to give spiro furan-pyrazoles. Their structure was confirmed by an X-ray crystallographic analysis on a derivative of the spiro furan-3(2H),5′(7′H)-pyrazolo 1,2-a∥1,2,4 triazole-1′,3′,6′-trione. The cycload-ducts show ring-open chain tautomerism.

Photodimerization of N-benzyl-1,4-dihydronicotinamide

Abstract N-benzyl-1,4-dihydronicotinamide dimerized on irradiation with λ=365nm across 2,3 and 5,6 double bonds to give the product I which closed to centro-symmetric cage dimer IV on further irradiation with λ⩽313nm.

Ring–chain isomerism of some 4,5-disubstituted pyridazines involving heterospiro-compounds

I.r., u.v., and 1H n.m.r. spectral evidence demonstrated that 5-(o-aminophenylcarbamoyl)pyridazine-4-carboxylic acid (4), for which the zwitterionic structure (4a) appeared the most likely in the solid state, existed in dimethyl sulphoxide solution nearly exclusively as 3′,4′-dihydro-3′-oxospiro[pyridazine-5(2H), 2′(1′H)-quinoxaline]-4-carboxylic acid (18). The equilibrium (4a)⇄(18) was strongly influenced by the nature of the solvent. A study of the behaviour of compounds (5)–(10) enabled us to establish that the spirocyclisation critically depends on both the nature of the substituents on the pyridazine ring and on the nucleophilicity of the group bonded to the phenyl ring.

A new route to highly substituted 1H-pyrrol-3(2H)-ones

Abstract Reaction of 3,4-diacetyl-3-hexen-2,5-dione, 1, with alkyl or aryl primary amines, 2a–g, led to highly substituted 1H-Pyrrol-3(2H)-ones, 3a–g. The structure was established from a single crystal X-ray analysis of compound 3c.

Selectivity in cycloadditions: Crystal and molecular structure of (1a,4β,5a)-1,5-diacetyl-4-hydroxy-4-methylbicyclo[3.1.0]Hexan-2-one

Abstract The stereochemistry of (1a,4β,5a)-1,5-diacetyl-4-hydroxy-4-methylbicyclo[3.1.0]hexan-2-one, the main cycloadduct of 2,3-diacetyl-4-hydroxy-4-methylcyclopent-2-en-1-one and diazomethane, was unambiguously established from a single crystal X-ray analysis.

Polyazaheterocyclic compounds: condensation reactions of pyridazine-4,5-dicarboxylic acid derivatives with o-phenylenediamine

Diethyl pyridazine-4,5-dicarboxylate (II) and its 3,6-dimethyl derivative (XIV) cyclised with o-phenylenediamine in the presence of sodium hydride to give 6,11-dihydropyridazino[4,5-c][1,6]benzodiazocine-5,12-dione (III) and its 1,4-dimethyl derivative (XV), respectively. By heating under reduced pressure these compounds were dehydrated to the corresponding pyridazino[4′,5′:3,4]pyrrolo[1,2-a]benzimidazol-11-ones (XII) and (XX).Compound (III) reacted with diazomethane yielding a mixture of di-N-methyl (IV), NO-dimethyl (V), and di-O-methyl (VI) derivatives. Mild alkaline hydrolysis of the dione (III) afforded 5-(o-aminophenylcarbamoyl)-pyridazine-4-carboxylic acid (VII), which cyclised to 5-(benzimidazol-2-yl)pyridazine-4-carboxylic acid (VIII). Heating compound (III) with hexamethylphosphoric triamide gave NN-dimethyl-5-(benzimidazol-2-yl)pyridazine-4-carboxamide (XI).3,6-Dimethylpyridazine-4,5-dicarboxylic anhydride (XVI) reacted with o-phenylenediamine at room temperature to give 3,6-dimethyl-5-(o-aminophenylcarbamoyl)pyridazine-4-carboxylic acid (XVII), whereas when refluxed with the same reagent in acetic acid it afforded 2-(3,6-dimethylpyridazin-4-yl)benzimidazole (XVIII).

New cyanofluorene derivatives as electron acceptors in semiconducting complexes

9,9′-Bifluorenylidene-3,3′,6,6′-tetracarbonitrile (TCBF) and (3,6-dicyano-9H-fluoren-9-ylidene)propanedinitrile (TCPF) have been synthesized starting from 9-oxo-9H-fluorene-3,6-dicarbonitrile. A 2 : 1 charge transfer complex of TCPF with NNN′N′-tetramethyl-p-phenylenediamine has been obtained, and the electrical and spectral properties investigated. Conductivity measurements performed on polycrystalline samples gave a value of the order of 0.02Ω–1 cm–1. These results support the ability of this new acceptor in forming charge-transfer complexes with semiconducting properties.

Hydrogen-bonding pathways affecting chemical reactivity of mandelylasparagine and related compounds

The different behaviour of L-(+)-N-mandelyl-L-(–)-asparagine, N-mandelyl-2-amino-4-pentanoic acid and N-mandelyl-2-aminobutanoic acid towards acylation was considered. 13C and 1H n.m.r. non-selective and selective relaxation rates and 1H-{1H} n.O.e.s were taken to show that L(+)-N-mandelyl-L-(–)-asparagine assumes, in DMSO solution, a conformation quite different from that of the other two amino acids. In this conformation both lone pairs of the alcoholic oxygen were shown to be involved in hydrogen bonding and to be shielded in a way that makes approach of the acylating reagent difficult.

Lanthanoid-induced shifts as a configurational tool for some bicyclo[3.1.0] hexane derivatives

The 1H n.m.r. spectra of 1,5-diacetyl-4-hydroxy-4-methylbicyclo[3.1.0]hexan-2-ones (2) and (3) and diethyl 4-hydroxy-4-methyl-2-oxobicyclo[3.1.0]hexane-1,5-dicarboxylate (6) were determined in the presence of the shift reagent Eu(fod)3. The observed induced shifts provide evidence for the relative configuration of the asymmetric centres of these compounds.