Hermann Irngartinger

Crystal Engineering with Symmetrical Threefold Acceptor-Substituted Triaminobenzenes

Is it possible to identify molecular architectures that allow prediction of crystal structures? Can the factors that determine these structures be identified? To answer these questions, analogues of 1, which forms layer structures, were synthesized in which some or all of the nitro groups were replaced with sulfonyl acceptors. Surprisingly, the expected drastic change in the conformational and/or crystallographic behavior was not observed.

Homolytic aziridine opening (aza variant of cyclopropylcarbinyl-homoallyl rearrangement) by addition of tributyltin radical to N-acylaziridines. Factors contributing to the regioselectivity

Abstract AIBN initiated reaction of N-acylaziridines 1 with Bu3SnH in refluxing benzene provided products 5 and 8 of reductive ring opening. Yields (practically quantitative in most cases) fell drastically with steric hindrance of the addition of Bu3Sn. to the acyl oxygen of 1. They depended to some extent on the experimental conditions for hydrogen capturing when aziridine homolysis provided a primary radical 3 or 6. The regioselectivity of (probably reversible) ring homolysis can be understood in terms of the stability of the arising radical (3, 6), of stereoelectronic control (e.g. 1i as compared to 1h) and of frontier orbital interactions (1j). A possible difference in bond lengths as explanation for the formation of the primary radical from 1j did not find support from an X-ray structure analysis of N-tosyl-2-methyl-aziridine 11. Isomeric products were obtained only twice (1i, 1j) with a dependence of the ratio 5j:8j on concentration and hydrogen isotope of Bu3SnH. No such dependence was found for the ratio 5:14 (reduction without and with an intervening cyclization of 3 leading to a pyrrolidone) obtained from the N-cinnamoylaziridine 11. This ratio (1:9 for 11 and 1:3 for 1n) must reflect the E-Z isomers in 3. The observed preference for the formation of E-3 from 2 can be explained by stereoelectronic and steric effects. A cinnamoyl double bond in 5 was saturated depending on experimental conditions.

Molecular structures of a seco-dodecahedradiene and an iso-dodecahedrane

Abstract The olefinic carbon atoms on the closed side of seco-dodecahedradiene 1 are strongly pyramidalized (o = 35.3°). The transanular C1C2 bond of non-pentagonal isododecahedrane 2 is one of the longest CC bonds (1.691A) ever measured in cage structures.

(1R,1′R)-di-born-2-eno[2,3-c;3′,2′-e][1,2]dithiin, ein cyclisches disulfid mit ungewöhnlichen eigenschaften

Abstract The title compound 8 , obtained by oxidation of bis-thiocamphor 6 , represents a kinetically stabilized disulfide. Despite deeply colored, as usual in the 1,2-dithiine series, 8 displays various other features in strict contrast to the normal behaviour of 1,2-dithiines. Thus, 8 prefers S-insertion to the 1,2,3-trithiepine 14 instead of S-extrusion to the thiophene 12 . Furthermore, ring opening by nucleophilic reagents is followed by 1,5-H-shifts leading to blue enthiones, e.g. 17 , 18 , and 19 .

Substituent Effects on Redox Properties and Photoinduced Electron Transfer in Isoxazolo‐Fullerenes

The new C60 and C70 adducts 1b, 1d-1k, 1m, 6d, 7d, and 8d have been synthesized by [2+3] cycloadditions of the appropriate nitrile oxides. Variations in the distance and geometry of the donor and acceptor substituents are seen to have an influence on the redox behavior of the fullerene adducts in cyclic voltammetry experiments. The isoxazolo-fullerenes 1c, 1d, and 1i show shifts of about 30 mV or 40 mV to more negative values compared with the reference compound 1a. On the other hand, strong acceptor properties are detected in the case of compound 1e, which shows a positive shift of 30 mV relative to 1a. Moreover, time-resolved fluorescence spectroscopy has shown that upon excitation of the fullerene moiety in the polar solvent benzonitrile, an electron is transferred from the donor substituent to the first excited singlet state of the fullerene, thereby reducing the excited-state lifetime. Our data demonstrate that the electron-transfer rate in donor-substituted fullerenes can be controlled by the electron-donating property of the substituent as well as the electronic structure and/or length of the spacer used. The C70 regioisomers 6d, 7d, and 8d exhibit differences in their spectroscopic characteristics.

Ring opening of the heterocycle in [60]fullereno[1,2-d]isoxazole

1-Cyano-2-hydroxy-dihydro[60]fullerene (2) was synthesized by NO-bond cleavage of the isoxazoline derivative [60]fullereno[1,2-d]isoxazole (1). The esterification of valeric acid with this fullerol produced valeric acid 2-cyano-fulleryl ester (3).

Photooxidation and Intramolecular Reaction of the Anthryl Moiety in [60]Fullerene Derivatives

Anthracene groups have been linked to [60]fullerene by the [3+2] cycloaddition of the corresponding nitrile oxides or by esterification with a [60]fullerenol. The anthryl groups of the fullerene derivatives 3, 7, and 10 react readily with singlet oxygen to form the 9,10-epidioxides 4, 8, and 12 under photooxidation. The anthryl moiety of the fullerenol ester 10 also reacts with the fullerene skeleton to form the stable intramolecular Diels-Alder adduct 11.

Preparation and properties of 1-thia-6-azacyclodeca-3,8-diynes

Abstract The preparation of two 1-thia-6-azacyclodeca-3,8-diynes is reported together with their spectroscopic and structural properties (X-ray structure).

Determination of the Electron Density Distribution in the Bonds of a Fullerene Derivative by High‐Resolution X‐Ray Structure Analysis

Bent bonds in the strained fullerene system, restricted to the [5,6] bonds, were detected by high-resolution X-ray structure analysis of the 1,2-dihydro[60]fullerene derivative 1. In addition the maxima of electron densities are higher in the [6,6] bonds than in the [5,6] bonds-an important finding with respect to the question of the extent of electron delocalization in fullerenes.

Strong electron acceptor properties of 3′(pentafluorophenyl)isoxazolo[4′,5′:1,2][60]fullerene derivatives

Abstract Investigations on the synthesis and electrochemical behaviour of a new class of acceptor substituted isoxazolofullerenes is described. The influence of distance and orientation of pentafluorophenyl substituents on cyclic voltammetry is discussed. The strong acceptor effect of 1c could be due to a through space interaction of a pentafluoro-phenyl substituent with the [60]fullerene surface.