1,3-Dipolar cycloaddition approach to isoxazole, isoxazoline and isoxazolidine analogues of C-nucleosides related to pseudouridine

Isoxazole, isoxazoline and isoxazolidine analogues of C-nucleosides related to pseudouridine have been synthesized by 1,3-dipolar cycloaddition reactions of nitrile oxides and nitrones derived from mono and disubstituted uracil-5-carbaldehydes and 2,4-dimethoxypyrimidine-5-carbaldehyde. The dimethoxy derivatives have been easily deprotected to the corresponding uracils bearing the heterocyclic ring instead of a sugar moiety. The regio and stereoselectivity of the reactions are discussed.     

1,3-Dipolar cycloaddition reactions of 2-phenyl-4-arylidene-5(4H)-oxazolones with nitrile oxides

Stable nitrile oxides are added stereospecifically and regioselectively to the carbon carbon double bond of 2-phenyl-4-arylidene-5(4H)-oxazolones resulting spiro-derivatives 3, 5 . The spectral properties of the reaction products are discussed. The cycloadducts give several substituted isoxazolines via an opening of the oxazolone ring with nucleophilic reagents.     

Synthesis, structural characterization and electrochemical study of 1,1′-ferrocenylene labeled amino acids

Unsymmetrical 1,1′-disubstituted ferrocenes bearing an amino acid moiety and a conjugated electron density controlling substituent were synthesized conveniently starting from 1,1′-ferrocenedicarbaldehyde. The novel ferrocene amino acid derivatives were completely characterized from their MS, ¹H NMR and ¹³C NMR spectra. Their electrochemical behavior was studied by cyclic voltammetry. Their formal redox potentials E_f were slightly influenced by the nature of the amino acid and mainly by the kind of the ethenyl substituent. Furthermore all the (Z)-isomers exhibited a slight anodic shift compared with the corresponding (E)-isomers.     

1,3-Dipolar cycloaddition approach to pyrrolidine analogues of C-nucleosides related to pseudouridine

Pyrrolidine analogues of C-nucleosides related to pseudouridine have been synthesized by 1,3-dipolar cycloaddition reactions of uracil-5 and 2,4-dimethoxypyrimidine-5 nitrones with allyl alcohol and methyl acrylate, and subsequent reductive cleavage of the isoxazolidine cycloadducts. The dimethoxy derivatives have been easily deprotected to the corresponding uracils bearing the pyrrolidine ring instead of a sugar moiety. The regio and stereoselectivity of the reactions are discussed.     

Labeling of organic biomolecules with ethynylferrocene

The Sonogashira coupling reaction of ethynylferrocene with adenine, uracil, tyrosine and steroid derivatives was studied; with the exception of tyrosine it was proved to be a good route for the attachment of ferrocene to these representative biomolecules. In addition the transformation of alkynyl uracil to furanopyrimidone derivatives was investigated and the formation of the furanopyrimidone ring was confirmed by an X-ray crystallographic analysis carried out on product 16.     

Diastereocontrol in the intramolecular cycloadditions of 2-substituted-erythro-3,4-isopropylidenedioxyhex-5-enenitrile oxides

The influence of the 2-substituent on the diastereoselectivity of the intramolecular cycloadditions in a series of 2-substituted-erythro-3,4-isopropylidene-dioxyhex-5-enenitrile oxides, generated in situ from selected sugar derivatives, was examined.     

1,3-Dipolar cycloaddition reactions of 4-arylidene-2-phenyl-1,4-dihydroimidazol-5-ones with nitrile oxides

Stable nitrile oxides add regioselectively to the carbon-carbon double bond of 4-arylidene-2-phenyl-1,4-dihydroimidazol-5-ones to afford spiro isoxazolines 3 . Compounds 3 are further hydrolysed to isoxazole derivatives.     

The reaction of triphenylphosphine with arylbromonitromethanes. Formation of arylnitriloxides.

Formation of furoxans and δ²-isoxazolines confirms that arylnitriloxides are intermediates in the reaction of arylbromonitromethanes with triphenylphosphine.     

1,3-dipolar cycloaddition of nitrile oxides with 2-phenyl-4-ethoxymethylene-5(4H)-oxazolone

2-Phenyl-4-ethoxymethylene-5(4H)-oxazolone 1 reacts regioselectively with nitrile oxides to give cycloadducts 3 . Reactions of the cycloadducts 3 with nucleophiles lead to 4-aminoisoxazole derivatives.