Ralf Keuper

Synthesis of porphyrin dimers using a Heck-type coupling reaction with bisacrylates

The Heck-type crosscoupling reaction in DMF under phase-transfer conditions of zinc(II)-monobromo-deuteroporphyrin-dimethylester (1) and several bifunctional α,β-unsaturated carbonyl compounds 3a-e provided CC-linked dimeric porphyrins, an important class of photosensitizers.

Efficient preparation of substituted 5,6,7,8-tetrahydroquinolines and octahydroacridine derivatives

The reaction of the enamine 4 with different β-amino ketone hydrochlorides 3a–e affords the diketones 5a–e which can be cyclized to the corresponding mono- and disubstituted tetrahydroquinolines 6a–e. Furthermore the preparation of the octahydroacridines 8f and 8g by using a straightforward multi step sequence is described.

Synthesis of Novel Functionalized Bi‐ and Oligopyridines

An annelation reaction is presented in which 1,3-cyclohexanedione (1) and Mannich bases 6a,b are used for the preparation of functionalized bipyridines 12a, 13a, 14a and dihydropyridine derivatives 10b, 11b. All these products possess a keto group which will allow further transformations. The same concept was applied for the synthesis of the S-shaped terpyridine 25. The reaction of the Mannich base 21 with 1,3-cyclohexanedione yielded the heptacyclic terpyridine 22, which is a key intermediate for the synthesis of torands and other tridentate clefts. The ketone 12a was used for the synthesis of the quaterpyridine 26.

Preparation, characterization and selective reactions of novel [1,3]diazetidine‐2,4‐diones (uretdiones) — a new route to generate asymmetric substituted toluylenediisocyanate‐derivatives

The selective cyclodimerization of monomeric diisocyanates like IPDI 4 and TDI 5 yields [1,3]diazetidine-2,4-diones (uretdiones). On this basis, a new method for the selective transformation of the NCO-groups of asymmetric substituted diisocyanates is described. The reaction with different nucleophiles yields carbamates and ureas such as 9–11.

Synthesis and Characterization of Novel Pyridines and 3,3′-Bridged Bipyridines Using 1,x-Cyclohexanediones

A one-pot reaction using 1,x-cyclohexanediones, a Mannich base (or its hydrochloride), and ammonium acetate delivers novel pyridines or 3,3′-bridged bipyridine compounds 8, 16, 18, 20, and 22. This strategy offers a great flexibility in the design of new building blocks, e.g. in supramolecular chemistry and underlines the efficiency of domino reactions.

Ruthenium(II)-Komplexe mit neuartigen 1,10-Phenanthrolinliganden / Ruthenium(II) Complexes with New Kinds of 1.10-Phenanthrolin Ligands

Different pathways to Ru-complexes are described using the hitherto unknown S-type terpyridines 3 and the known U-type ligands 4. The resulting hexafluorophosphates 6 and 7 have been spectroscopically characterized by 1H NMR and IR data and also by mass spectrometry and cyclic voltammetry.