Siegfried Blechert

Heterogeneous catalysis for trifluoromethylations and perfluoroalkylations has been performed. Through the usage of cheap, metal‐free and recyclable mesoporous graphitic carbon nitride (mpg‐CN) it was possible to fluoroalkylate various arenes by the reductive activation of sulfonyl chlorides with visible light. Thus, we were able to demonstrate the robustness and versatility of mpg‐CN as a photoredox catalyst beyond water splitting and the activation of oxygen.

Mesoporous graphitic carbon nitride (mpg‐C₃N₄) was found to be an efficient heterogeneous photocatalyst for the metal‐free radical cyclization of 2‐bromo‐1,3‐dicarbonyl compounds. Reactions leading to functionalized cyclopentanes proceed under mild conditions and can be conducted in a continuous flow photoreactor. Compared to the batch reaction, the use of a continuous flow reactor resulted in a significant reduction in reaction time (complete conversion of 0.04 mmol of substrate in a batch was achieved after 4 h, whereas in a flow reactor the same amount of substrate was fully converted into a product within 40 min). Mechanistic studies of the reaction showed that THF plays not only the role of solvent, but is also a crucial hydrogen and electron donor.

Within the last couple of years, the photocatalytic, oxidative CC coupling has grown to a well‐established methodology, especially for the modification of aryl‐substituted tetrahydroisoquinoline derivatives. However, until now, this reaction is mainly restricted to the usage of strong nucleophiles like nitroalkanes, cyanides, enamines, phosphonates and malonates. Within this publication we present an extension of such a method towards the application of weaker nucleophiles, namely allylstannanes, allylsilanes and allylboranes. Therefore, a very simple protocol was invented, using heterogeneous mesoporous graphitic carbon nitride (mpg‐C₃N₄) as catalyst and air as oxidizing agent, leading to high yields for a broad range of substrates. magnified image

New bimetallic Zn/Zr salen-type systems were employed as catalysts in the asymmetric intramolecular hydroamination reaction. High enantioselectivity for the formation of piperidines of up to 98% ee were observed.

Microporous polymer networks based on binaphthyl phosphoric acids are suitable heterogeneous asymmetric organocatalysts. Herein we show that the porous characteristics of such networks can be fine-tuned by co-polymerisation. This enables us to investigate the influence of the surface area and porosity in microporous networks on their catalytic performance. In this case, the activity of the polymers in an asymmetric hydrogenation reaction is increased by the use of polymers with higher surface areas.

This publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.

Herein, we report on the first enantioselective synthesis of the sparteine‐type alkaloids virgidivarine (1) and virgiboidine (2). The stereoselective construction of the challenging dipiperidine core within 1 and 2 was realized by applying an intramolecular ene‐ene‐yne ring‐rearrangement metathesis (RRM) protocol. In combination with this sequence, an unprecedented tandem metathesis/oxidation reaction was established. Subsequent to the RRM event, the Ru‐alkylidene species was converted into the highly potent dihydroxylation catalyst RuO₄ by the addition of NaIO₄. This transformation rendered five sequential reactions that include an ene‐ene‐yne RRM/dihydroxylation/glycol cleavage in a one‐pot procedure. This approach provides practical and general access to dipiperidines and piperidino‐quinolizidines. Despite their wide use in organic and organometallic chemistry as well as their occurrence in biologically active natural products, methods are still lacking for the stereoselective synthesis of these motifs.

A relay catalysis of a cationic zinc complex and N,N‐dimethylaniline hydrotrifluoromethyl sulphonate induces a multiple CC bond and CN bond formation. The one‐step synthesis make highly substituted bi‐ and tricyclic 1,2‐dihydroquinoline derivatives easily available from simple starting materials. The high yielding process consists of several simultaneous operating steps.

In this communication we describe the oxidative CC bond formation of tertiary amines with various nucleophiles under very mild and environmental friendly conditions by using mesoporous graphitic carbon nitride (mpg‐C₃N₄) semiconductor as a heterogeneous, metal‐free photosensitizer in combination with visible light and oxygen as the terminal oxidation agent. This system can be further combined with proline‐organocatalysis to achieve oxidative tandem photocatalysis, demonstrating a rich cascade of chemical possibilities of the current photosynthesis system.