Abstract

Abstract

Abstract

Abstract

Triarylmethylium tetrafluoroborates with a sterically shielded cationic center react with selected C- and N-nucleophiles under nucleophilic aromatic substitution to give dipolar p-quinoid final products. The mechanistic rationale includes a hydride leaving group in analogy to the Tschitschibabin reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The photochemical transformation of the monostyrylcalix[4]arenes 12a and 12b either leads to inherent chiral calix[4]phenanthrenes 13a and 13b under basic reaction conditions or to unexpected products of an acid-catalyzed ring cleavage of the macrocycle. Studies towards the reaction mechanism and the optimization of the reaction conditions are presented.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The concept for a new class of nonplanar polyaromatic hydrocarbons — the funnelenes — is presented. Retrosynthetic considerations lead to polyphenyl- and oligophenylcalix[4]arenes as potential precursors. In this paper we describe the synthesis of these calixarenes and the first cyclodehydration studies on a model compound which leads to a hexabenzocoronene derivative. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Triarylmethyl cations with a sterically shielded cationic center react with selected C- and N-nucleophiles under nucleophilic aromatic substitution. The resulting dipolar p-quinodimethanes represent highly functionalized extended π systems. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

For the reaction of α,β-unsaturated ketones with electron-rich arenes catalyzed by gold(III) chloride both, a Friedel–Crafts-type mechanism and an initial metallation, are evaluated. Gold(III) chloride has proven to be an efficient catalyst under very moderate reaction conditions, however, in the case of sterically demanding products HBF₄ turned out to be the superior catalyst.

We investigated a simple and economic method for the selective O-arylation of calix[4]arenes with N-heteroarenes with temperature control under neat conditions. The resulting multidentate ligands are potential building blocks for transition metal complexes or supramolecular aggregates: dipyridoxycalixarene 3b, together with palladium(II) chloride, produced a complex with a fascinating crystal structure, six molecules self-assembling into hexameric supracycles with an outer diameter of roughly 30 Å and an inner diameter of roughly 7 Å, containing six dichloromethane molecules. The supracycles themselves are organised into hexagonal assembled tubes along the c axis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

2-Iodocyclopentenones undergo a Heck reaction with allylic and homoallylic alcohols, in acceptable yields, to give dicarbonyl compounds useful for the construction of annulated cyclopentanones. In contrast, the corresponding iodo-substituted cyclohexenones, cycloheptenones and acyclic α,β-unsaturated ketones are far less or even unsuitable for Heck reactions of this type.