An effective synthesis of 2‐oxo‐1,3‐propanedial monohydrate or mesoxaldehyde (6a) and the first synthesis of 2,3‐dioxo‐1,4‐butanedial (18) as a thiane derivative are reported. These first members of the smallest vicinal tri‐ and tetracarbonyl compounds are stabilized by conversion to thiane derivatives 8, 9, 10, 11, 12, 15 and 19, which can be isolated as long‐lived compounds at room temperature. The structures of these novel thianes 8, 10, 12 and 15 were confirmed by their X‐ray crystal structures. The synthesis of a series of protected as well as free heterocyclic aldehydes (pterins and quinoxalines) by the use of the appropriate tricarbonyl compounds is also reported. Additionally, a one‐step synthetic strategy to prepare a series of different biheterocycles with the smallest vicinal tetracarbonyl compound is demonstrated.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The syntheses in good yields of some new difunctionalized 1,8-naphthyridines 4, 6, 8 and 9 and a novel triethylene glycol ether-linked dinaphthyridine, 10a, along with the mononaphthyridine-linked ether alcohol 10b are described. An improved and milder method for the synthesis of 2,7-diamino-1,8-naphthyridine (14) is also reported.

Single crystal X-ray structures of new perchlorate salts of a series of four xanthine alkaloids, for example, xanthine (xt), caffeine (cf), theophylline (tp), and theobromine (tb) are reported. The treatment of xanthine derivatives with 70% of HClO 4 afforded their salts Hxt 3 ClO 4 3 2(H 2 O), 1; Htp 3 ClO 4 , 2; Htb 3 ClO 4 , 3; and Hcf 3 ClO 4 3 H 2 O, 4. Xanthine form dimers via N(9)-H 3 3 3 O-C( 6) hydrogen bond in the crystal structure. Of the two possible resonance structures of the protonated imidazoles, one of the structures was found to be major in xanthine, theobromine, and caffeine salts, while both structures are of equal contribution in theophylline salts. These observations also have been verified by using the structural information available in the Cambridge Structural Database. Interestingly, xanthine 1 is present as a dihydrate and 4 as a monohydrate, whereas 2 and 3 are crystallized without any water. Thus, proton transfer from the strong acid HClO 4 to the weakly basic imidazole ring of xanthines occurs which leads to the build up of H-bonded supramolecular networks.

No abstract

Metal-superoxo species have attracted much attention recently as key intermediates in enzymatic and biomimetic oxidation reactions. The effect(s) of axial ligands on the chemical properties of metal-superoxo complexes has never been explored previously. In this study, we synthesized and characterized chromium(III)-superoxo complexes bearing TMC derivatives with pendant pyridine and imidazole donors, such as [Cr(III)(O2)(TMC-Py)](2+) (1, TMC-Py = 4,8,11-trimethyl-1-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane) and [Cr(III)(O2)(TMC-Im)](2+) (2, TMC-Im = 4,8,11-trimethyl-1-(2-methylimidazolmethyl)-1,4,8,11-tetraazacyclotetradecane). The reactivity of chromium(III)-superoxo complexes binding different axial ligands, such as 1, 2, and [Cr(III)(O2)(TMC)(Cl)](+) (3, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was then investigated in C-H bond activation and oxygen atom transfer reactions. Kinetic studies revealed that the reactivity of the Cr(III)-superoxo complexes depends on the axial ligands, showing the reactivity order of 1 > 2 > 3 in those electrophilic oxidation reactions. It was also shown that there is a good correlation between the reactivity of the chromium(III)-superoxo complexes and their redox potentials, in which the redox potentials of the chromium(III)-superoxo complexes are in the order 1 > 2 > 3. DFT calculations reproduced the reactivity order between 1 and 3 in both C-H bond activation and oxygen atom transfer reactions, and the latter reaction is described using orbital interactions. The calculations are also in agreement with the experimentally obtained redox potentials. The present results provide the first example showing that the reactivity of metal-superoxo species can be tuned by the electron-donating ability of axial ligands bound trans to the metal-superoxo moiety.