Dieter Lentz

Experimental electron density of sumanene, a bowl-shaped fullerene fragment; comparison with the related corannulene hydrocarbon

The experimental electron density of sumanene, C(21)H(12), was extracted from a high resolution X-ray data set measured at 100 K and topologically analyzed. In addition to bond topological and atomic properties, information about the density distribution between adjacent molecules, which show close C···C approaches of ~3.4 Å within the columnar π-stacks in the crystal lattice, are discussed. A comparison is made with the electron density of the related corannulene molecule based also on the analysis of Electron Localizability Indicator (ELI-D) calculations.

Equipping metallo-supramolecular macrocycles with functional groups: assemblies of pyridine-substituted urea ligands.

A series of di-(m-pyridyl)-urea ligands were prepared and characterized with respect to their conformations by NOESY experiments and crystallography. Methyl substitution in different positions of the pyridine rings provides control over the position of the pyridine N atoms relative to the urea carbonyl group. The ligands were used to self-assemble metallo-supramolecular M(2)L(2) and M(3)L(3) macrocycles which are generated in a finely balanced equilibrium in DMSO and DMF according to DOSY NMR experiments and ESI FTICR mass spectrometry. Again, crystallography was used to characterize the assemblies. Methyl substitution in positions next to the pyridine nitrogen prevents coordination, while the other ligands form small metallo-supramolecular macrocycles. The incorporated urea carbonyl groups provide hydrogen bonding sites which converge towards the center of the assemblies.

Synthesis of the Smallest Axially Chiral Molecule by Asymmetric Carbon–Fluorine Bond Activation

Surprisingly, thecarbon backbones of 3 and 5adeviate by 4.4(3)8 and 4.6(2)8from the linearity that would be expected based on their sp-hybridized central carbon atoms (Figure 2). Furthermore, thetwo terminal F-C-H planes in5a have a torsion angle of91.9(2)8. The previously reported structures derived frommicrowave spectroscopy do not show the same distortions(Supporting Information, Table S2), because erroneously, therefinement was based on a constrained linear geometry.

Corannulenylferrocenes: towards a 1D, non-covalent metal–organic nanowire

A class of novel corannulene-derived ferrocene donor-acceptor systems has been synthesized by straight-forward Negishi-type coupling of iodocorannulene. Their solid state structures have been studied crystallographically and found to exhibit unique inter- and intramolecular slipped stacking interactions.

Synthesis of Trifluorostyrene Derivatives by Palladium‐Catalyzed Cross‐Coupling of Lithium Trimethoxy(trifluorovinyl)borate with Aryl Bromides

Trifluorostyrene (TFS) derivatives have been widely used as monomers for the preparation of polymers with fluorinated backbones. However, they have seen little use in other research fields, such as medicinal chemistry, probably due to the lack of a convenient preparative method. Most previous syntheses of TFS derivatives have involved multistep reaction sequences, often involving unstable reagents or intermediates and suffering from low overall yields. g,3] As a more direct synthetic route, the palladium-catalyzed crosscoupling of trifluorovinyl zinc reagents or trifluorovinyl tin reagents with aryl iodides has been described. 4] Recently, a palladium-catalyzed reaction of tetrafluoroethylene (TFE) with arylzinc compounds has been reported to give TFS derivatives in moderate yields. Although these catalytic methods are more efficient than other multistep approaches, their broad applicability suffers from the use of toxic and unstable reagents, such as organostannanes, organozinc reagents, or gaseous and explosive tetrafluoroethylene. Organoboron compounds have found widespread use in palladium-catalyzed Suzuki–Miyaura coupling reactions because they are easy to prepare, stable, and have relatively low toxicity. In the context of TFS derivatives only two examples for the coupling of potassium (trifluorovinyl)trifluoroborate have been described so far. Very recently, the coppermediated coupling of potassium (trifluoromethyl)trimethoxyborate with aryl iodides has been reported. Herein, we report an efficient and convenient method for the introduction of a trifluorovinyl group based on the palladium-catalyzed Suzuki–Miyaura cross-coupling reaction. This procedure employs stable borate 1 as the source of the trifluorovinylgroup and, thus, circumvents the inconvenient use of highly unstable TFE, toxic stannanes, or sensitive zinc reagents (Scheme 1).

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

Summary An approach to enantiopure hydroxylated 2H-1,2-oxazine derivatives is presented utilizing the [3 + 3] cyclisation of lithiated alkoxyallenes and an L-erythrose-derived N-glycosyl nitrone as precursors. This key step proceeded only with moderate diastereoselectivity, but allowed entry into both enantiomeric series of the resulting 3,6-dihydro-2H-1,2-oxazines. Their enol ether double bond was then subjected to a hydroboration followed by an oxidative work-up, and finally the auxiliary was removed. The described three-step procedure enabled the synthesis of enantiopure hydroxylated 1,2-oxazines. Typical examples were treated with samarium diiodide leading to enantiopure acyclic aminopolyols. We also report on our attempts to convert these compounds into enantiopure hydroxylated pyrrolidine derivatives.

Linear and cyclic amides with a thiophene backbone: ultrasound-promoted synthesis and crystal structures.

A full synthetic study of linear and cyclic thiophene oligoamides has been carried out. The combination of an ultrasonic technique to diminish the intramolecular backfolding of longer oligoamide chains, therefore enhancing the accessibility of the carboxylic acid, and T3P as coupling reagent led to shorter reaction time and higher yields for both linear and cyclic oligoamides. By controlling the degree of dilution, macrocyclic amides with different sizes can selectively be prepared. Different crystal structures of cyclic thiophene oligoamides were also analyzed.