Jonathan O. Bauer

Organocatalytic, Oxidative, Intermolecular Amination and Hydrazination of Simple Arenes at Ambient Temperature

New atom-economical, environmental friendly, direct oxidative intermolecular processes of amination and hydrazination of nonprefunctionalized arenes were developed. The products were formed in a good regioselective manner under organocatalytic conditions at ambient temperature.

Highly Enantioselective Catalytic [6+3] Cycloadditions of Azomethine Ylides

Stereocontrolled cycloaddition reactions give efficient access to bioactive cyclic molecules 3] through concerted formation of two bonds and several stereocenters in one step. In particular, the reaction of activated alkenes with azomethine ylides derived from amino acids and aldehydes is a powerful method for the highly stereoselective synthesis of substituted pyrrolidines [Eq. (1)] bearing up to four stereogenic

Catalytic enantioselective synthesis of functionalized tropanes reveals novel inhibitors of hedgehog signaling.

Dipolar cycloaddition: A highly efficient copper(I)-catalyzed enantioselective [3+2] cycloaddition reaction of 1,3-fused cyclic azomethine ylides and nitroalkenes has been developed. This method provides access to functionalized tropane scaffolds with several quaternary and tertiary stereocenters in a single step under mild reaction conditions.

Discovery of Inhibitors of the Wnt and Hedgehog Signaling Pathways through the Catalytic Enantioselective Synthesis of an Iridoid-Inspired Compound Collection†

Cousins you can count on: An iridoid-inspired compound collection was synthesized efficiently by the resolution of cyclic enones in an asymmetric cycloaddition with azomethine ylides. The collection contained novel potent inhibitors of the Wnt and Hedgehog signaling pathways.

Biology‐Oriented Synthesis of a Withanolide‐Inspired Compound Collection Reveals Novel Modulators of Hedgehog Signaling

Biology-oriented synthesis employs the structural information encoded in complex natural products to guide the synthesis of compound collections enriched in bioactivity. The trans-hydrindane dehydro-δ-lactone motif defines the characteristic scaffold of the steroid-like withanolides, a plant-derived natural product class with a diverse pattern of bioactivity. A withanolide-inspired compound collection was synthesized by making use of three key intermediates that contain this characteristic framework derivatized with different reactive functional groups. Biological evaluation of the compound collection in cell-based assays that monitored biological signal-transduction processes revealed a novel class of Hedgehog signaling inhibitors that target the protein Smoothened.

Silyl‐Modified Analogues of 2‐Tritylpyrrolidine: Synthesis and Applications in Asymmetric Organocatalysis

Silicon-based organocatalysts: In an effort to study the effects of substituting carbon by silicon within the catalyst backbone, we developed an efficient synthesis of (S)-2-triphenylsilylpyrrolidine [(S)-2]. The evaluation of (S)-2 against its carbon analogue (S)-1 in two organocatalytic reactions is complemented by computational studies.

A Cyclization–Rearrangement Cascade for the Synthesis of Structurally Complex Chiral Gold(I)–Aminocarbene Complexes

A facile synthesis of chiral cyclic alkyl aminocarbene-gold(I) complexes from gold-free 1,7-enyne substrates was developed. The novel cyclization-rearrangement reaction sequence is triggered by the addition of (Me2S)AuCl to different 1,7-enynes and leads to structurally unique carbene-gold(I) complexes in high yields. These novel complexes are catalytically active and inhibit the proliferation of different human cancer cell lines.

Antibacterial and antiplasmodial constituents of Beilschmiedia cryptocaryoides.

Four new beilschmiedic acid derivatives, cryptobeilic acids A-D (1-4), and tsangibeilin B (5) have been isolated from the bark of Beilschmiedia cryptocaryoides collected from Madagascar. Their structures were elucidated using detailed spectroscopic and spectrometric methods. Cryptobeilic acid A (1) and tsangibeilin B (5) structures were confirmed by single-crystal X-ray diffraction analysis. Compounds 1-5 displayed moderate antibacterial activity against Escherichia coli 6r3, Acinetobacter calcoaceticus DSM 586, and Pseudonamas stutzeri A1501, with the minimum inhibitory concentrations ranging from 10 to 50 μM, respectively. In addition, the compounds exhibited antiplasmodial activity against erythrocytic stages of chloroquine-resistant Plasmodium falciparum strain NF54 and weak cytotoxicity against L6 cell lines.

Stereoselective Synthesis of Silicon‐Stereogenic Aminomethoxysilanes: Easy Access to Highly Enantiomerically Enriched Siloxanes

A route towards the synthesis of N,O-functionalized silicon-stereogenic organosilanes with excellent optical purities has been developed. Investigations into the stereoconvergence and configurational stability of an aminomethoxysilane suggest a kinetically controlled multistep substitution mechanism. Selective exchange of the Si-N bond by a second Si-O bond builds the basis for the controlled formation of chiral siloxane units with different oxygen-containing functional groups. Subsequent reactions of the chiral aminomethoxysilanes with hydroxy groups support a general inversion mechanism at the asymmetrically substituted silicon atom of N,O-functionalized organosilanes.

Stereocontrol in nucleophilic substitution reactions at silicon: the role of permutation in generating silicon-centered chirality.

Intramolecular isomerization in pentacoordinate compounds can play an essential role for the adjustment of defined stereochemical information. Here, we present a conclusive mechanism of a stereocontrolled reaction on chiral dimethoxysilanes that opens new aspects in understanding the origin of creating silicon-centered chirality during a nucleophilic substitution process. By combining experimental, structural, and quantum chemical methods, we were able to disclose an interconversion process, based on consecutive Berry-type motions, as the most plausible mechanism for describing the stereochemical outcome in suchlike substitution reactions.