Giorgio Adembri

Influence of the solvent on the stereoselectivity of 1,3-dipolar cycloaddition of nitrile oxides on several 4-substituted 2-cyclopentenones

The diastereofacial selectivity in 1,3-dipolar cycloadditions of 2,6-dichlorobenzonitrile oxide on 2-cyclopentenones 1–5 is strongly dependent on the solvent when an hydroxyl group is present at C(4) (1–2) while if this group is protected (3–4) or absent (5) the reaction is solvent independent.

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.

Synthesis of enantiopure bis-isoxazolines from (4R)-(+)-4-acetoxycyclopent-2-enone

Abstract (4 R )-(+)-4-Acetoxycyclopent-2-enone was used as a starting material in the stereoselective synthesis of enantiopure bis-isoxazolines.

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).

Photochemistry of 1-(2,6-dichlorobenzyl)-1,4-dihydronicotinamide

Abstract The cleavage of the N-benzyl bond characterizes the photochemical behaviour of I in methanol. Beside the coupling or the hydrogen abstraction products, the interconvertible 1,4,5,6-tetrahydropyridines VIa and VIb were obtained.

BH3 THF reduction of 3-methylisoxazolo [4,5-c]pyridines

Abstract 3-Methylisoxazolo[4,5-c]pyridine 1 on reduction with BH3:THF gave, via the isolable complex 4 , the tetrahydroisoxazolopyridine 5 . The presence of two chlorine atoms at the 4 and 6 positions directed borane attact to the isoxazole ring, yielding the aminoethylpyridine 8 . Both types of reduction were obtained with 6-chloroisoxazolo[4,5-c]pyridine 7 .

Regio- and diastereo-selectivity in 1,3-dipolar cycloadditions of nitrile oxides to 4-substituted cyclopent-2-enones

The behaviour of 4-hydroxy-4-methylcyclopent-2-enone and related 4-substituted cyclopent-2-enones towards 1,3-dipolar cycloaddition with nitrile oxides is studied. The reactions are always completely regioselective while the diastereofacial selectivity depends on the nature of the substituents. Remarkably, the reaction of 4-acetoxycyclopent-2-enone shows complete regio- and diastereo-facial selectivity.