[en] Short communication

[en] The published data on the use of 1,3-dipolar cycloaddition reactions of nitrile oxides in the synthesis of natural compounds and their analogues are systematised and reviewed. The bibliography includes 145 references.

No abstract available

[en] Elimination reactions of (E)-2,4-(NO₂)₂C₆H₂CH=NOC₆H₃-2-X-4-NO₂ (1a-e) promoted by R₃N/R₃NH⁺ in 70 mol % MeCN(aq) have been studied kinetically. The reactions are second-order and exhibit Bronsted β = 0.80-0.84 and |β_lg| = 0.39-0.42, respectively. For all leaving groups and bases employed in this study, the β and |βlg| values remained almost the same. The results can be described by a negligible p_xy interaction coefficient, p_xy = ∂β/pK_lg = ∂β_lg/pK_BH ∼ 0, which describes the interaction between the base catalyst and the leaving group. The negligible p_xy interaction coefficient is consistent with the (E1cb)_irr mechanism. Change of the base-solvent system from R₃N/MeCN to R₃N/R₃NH⁺-70 mol % MeCN(aq) changed the reaction mechanism from E2 to (E1cb)_irr. Noteworthy was the relative insensitivity of the transition state structure to the reaction mechanism change

[en] Natacha Betz has participated to the creation of the IRAP conference series and co-organized three of them. Unfortunately, ten years ago, she passed away. The organization of IRAP 2016 in France gives us the opportunity to pay a tribute to her memory.

[en] Elimination reactions of (E)-2,4,6-(NO_2)_3C_6H_2CH=NOC(O)C_6H_4X (3) promoted by R_2NH/R_2NH_2"+ in 70 mol% MeCN (aq) have been studied. The reactions produced elimination products and exhibited second-order kinetics. The β and |β_l_g| values remained nearly the same for all leaving groups and bases. The results can be described by the negligible p_x_y interaction coefficient, p_x_y = ∂β/∂pK_l_g = ∂β_l_g/∂pK_B_H ≈ 0, which provides a strong support for the (E1cb)_i_r_r mechanism. For eliminations from (E)-ArCH=NOC(O)C_6H_4X (1, 3) and (E)-2,4,6-(NO_2)_3C_6H_2CH=NOAr' (2, 3), the change of the β-aryl group (Ar) from 2,4-dinitrophenyl (1) to 2,4,6-trinitrophenyl (3) increased the rate by 270-fold without appreciable change in the transition state structure. On the other hand, the leaving group (OAr') variation from benzoate (3) to 4-nitrophenoxy (2) induced a change in reaction mechanism from (E1cb)_i_r_r to E2. These results have been attributed to the cyclic transition state for the nitrile-forming eliminations involving the benzoate leaving group.

[en] The concise synthesis of a novel chiral diyne substrate for the assembly of chiral naphthylpyridines was described and different conditions for the cobalt-catalyzed co-cyclotrimerization with nitriles investigated. The products are novel naphthylpyridines possessing configurationally stable biaryl axes. Graphical abstract: .

No abstract available

[en] 1-hydroxybenzotriazole derivatives are used with carbodiimide as additives to generate active esters during peptide bond formation. They are also used as additives during the peptide bond formation. Dissociation constants of the 1-hydroxybenzotriazole (HOBt) and its derivatives, 1-hydroxy-6-chloro benzotriazole, 1-hydroxy-6-trifluoro methylbenzotriazole, 1-hydroxy-6-nitrobenzo-triazole were determined spectrophotometrically in 95% acetonitrile-water. In addition, 7-aza-1-hydroxybenzotriazole (7-HOAt) and 4-aza-1-hydroxybenzotriazole (4-HOAt) were also studied. Recently, oxyma was reported as a good replacement for the benzotriazole derivatives. As alcoholic components of active esters, the oximes seem to be good leaving groups. Therefore it was expected, that the strongly acidic and nucleophilic oximes, which possess electron-withdrawing groups in the molecule, are suitable as additives during the peptide bond formation. The dissociation constant of some oximes, such as diethyl 2-(hydroxyimino)malonate, ethyl 2-cyano-2-(hydroxyimino)acetate (oxyma), hydroxycarbonimidoyl dicyanide and N-hydroxypicolinimidoyl cyanide in 95% acetonitrile-water are reported. (author)

[en] We have studied the nitrile-forming elimination reactions from 1 promoted by R₂NH in MeCN. The reaction proceeded by (E1cb)_irr mechanism. Change of the β-aryl group from 2,4-dinitrophenyl to a more strongly electron-withdrawing 2,4,6-trinitrophenyl increased the reaction rate by 470-fold, shifted the transition state toward more reactant-like, and changed the reaction mechanism from E2 to (E1cb)_irr. To the best of our knowledge, this is the first example of nitrile-forming elimination reaction that proceeds by the (E1cb)_irr mechanism in MeCN. Noteworthy is the carbanion stabilizing ability of the 2,4,6-trinitrophenyl group in aprotic solvent. Nitrile-forming elimination reactions of (E)-benzaldoxime derivatives have been extensively investigated under various conditions. The reactions proceeded by the E2 mechanism in MeCN despite the fact that the reactants have syn stereochemistry, poor leaving, and sp² hybridized β-carbon atom, all of which favor E1cb- or E1cb-like transition state. Moreover, the transition state structures were relatively insensitive to the variation of the reactant structures. The results have been attributed to the poor anion solvating ability of MeCN, which favors E2 transition state with maximum charge dispersal. For eliminations from strongly activated (E)-2,4-(NO₂)₂C₆H₃CH=NOC(O)C₆H₄X, a change in the reaction mechanism from E2 to (E1cb)_irr was observed as the base-solvent was changed from R₂NH in MeCN to R₂NH/R₂NH₂⁺ in 70 mol % MeCN(aq). A combination of a strong electron-withdrawing β-aryl group and anion-solvating protic solvent was required for the mechanistic change