Johannes C. L. Walker

Georg-August-Universität Göttingen | GAUG · Institute of Organic and Biomolecular Chemistry

Saturated bioisosteres of substituted benzenes offer opportunities to fine-tune the properties of drug candidates in development. Bioisosteres of para -benzenes, such as those based on bicyclo[1.1.1]pentane, are now very common and can be used to increase aqueous solubility and improve metabolic stability, among other benefits. Bioisosteres of orth...

Indem sie Alkene in Carbonyle und Diole umsetzen, könnten nitrofunktionalisierte Aromaten gängige Oxidationsmittel ersetzen. Die Reaktionen laufen photochemisch bei niedriger Temperatur – und mechanistisch teils anders als die klassischen Varianten.

Saturated bridged-bicyclic compounds are currently under intense investigation as building blocks for pharmaceutical drug design. However, the most common methods for their preparation only provide access to bridgehead-substituted structures. The synthesis of bridge-functionalised species is highly challenging but would open up many new opportuniti...

Bicyclo[2.1.1]hexanes are a versatile platform for the exploration of chemical space, with 10 different substituent vectors available. Disubstituted bicyclo[2.1.1]hexanes have been proposed as bioisosteres of ortho- and meta-substituted benzenes, both far less investigated than their para-benzene counterparts, but the bicyclo[2.1.1]hexane platform...

Bicyclobutanes are among the most highly strained isolable organic compounds and their associated low activation barriers to reactivity make them intriguing building-blocks in organic chemistry. In recent years, numerous creative synthetic strategies exploiting their heightened reactivity have been presented and these discoveries have often gone ha...

A visible‐light organophotocatalytic [2+2] cycloaddition of electron‐deficient styrenes is described. Photocatalytic [2+2] cycloadditions are typically performed with electron‐rich styrene derivatives or α,β‐unsaturated carbonyl compounds, and with transition‐metal‐based catalysts. We have discovered that an organic cyanoarene photocatalyst is able...

A visible light organophotocatalytic [2+2] cycloaddition of electron-deficient styrenes is described. Photocatalytic [2+2] cycloadditions are typically performed with electron-rich styrene derivatives or α,β-unsaturated alkenes, and with transition-metal-based catalysts. We have discovered that an organic cyanoarene photocatalyst is able to deliver...

A route to prepare functionalized quinolines based on a Heck reaction/UV-induced alkene isomerization sequence is described. The method allows for the preparation of quinolines under mild and neutral conditions and has broad functional group tolerance. Acid-sensitive functional groups that would not be tolerated under previous approaches can be inc...

A current research program in our laboratory is devoted to the development of cyclohexa-1,4-diene-based surrogates of difficult-to-handle compounds and their application in metal-free ionic transfer reactions. These investigations grew from our interest in silylium ion chemistry and consequently concentrated initially on surrogates of gaseous and e...

Silylium ions, or, to be more precise, donor-stabilized silylium-ion-like species, were once only the domain of computational and structural chemists. This was mainly due to the difficulties in generating and isolating these reactive species in a condensed phase. Even chemists focused on reactivity stayed away from such delicate ions. The state of...

A photochemical approach to polysubstituted heterocycles using UV‐induced alkene isomerization is described. The method allows for the synthesis of disubstituted furans and pyrroles under mild and neutral conditions and also provides access to a class of trisubstituted furans pertinent to natural‐product synthesis. The method has broad functional‐g...

The design and gram‐scale synthesis of a cyclohexa‐1,4‐diene‐based surrogate of isobutene gas is reported. Using the highly electron‐deficient Lewis acid B(C6F5)3, application of this surrogate in the hydromethallylation of electron‐rich styrene derivatives provided sterically congested quaternary carbon centers. The reaction proceeds by C(sp³)−C(s...

The design and gram‐scale synthesis of a cyclohexa‐1,4‐diene‐based surrogate of isobutene gas is reported. Using the highly electron‐deficient Lewis acid B(C6F5)3, its application in the hydromethallylation of electon‐rich styrene derivatives to provide sterically congested quaternary carbon centers was achieved. The reaction proceeds by C(sp3)–C(s...

The design and a gram-scale synthesis of a bench-stable cyclohexa-1,4-diene-based surrogate of gaseous hydrogen iodide are described. By initiation with a moderately strong Bronsted acid, hydrogen iodide is transferred from the surrogate onto C-C multiple bonds such as alkynes and allenes without the involvement of free hydrogen iodide. The surroga...

A regioselective hydrodeuteration of alkenes using monodeuterated cyclohexa-1,4-dienes as surrogates for hydrogen deuteride (HD) gas is reported. The metal-free process proceeds under B(C6F5)3 catalysis presumably by deuteride abstraction to form borodeuteride [DB(C6F5)3]- and highly Brønsted-acidic Wheland intermediates. Low catalyst loadings (2.5...

A short (10 step) and efficient (15% overall yield) synthesis of the natural product (−)-(3R)-inthomycin C is reported. The key steps comprise three C–C bond-forming reactions: (i) a vinylogous Mukaiyama aldol, (ii) an olefin cross-metathesis reaction, and (iii) an asymmetric Mukaiyama–Kiyooka aldol. This route is notable for its brevity and has th...

Over the last few years, a number of olefin metathesis catalysts have been disclosed that enable the synthesis of energetically disfavoured Z-alkenes. The application of this method to the synthesis of complex natural products has driven the development of new catalysts and furthered the understanding of their behaviour and reactivity. This digest...