CAAC-Based Thiele and Schlenk Hydrocarbons

Diradicals have been of tremendous interest for over a century ever since the first reports of p- and m-phenylene-bridged diphenylmethylradicals in 1904 by Thiele and 1915 by Schlenk. Reported here are the first examples of cyclic(alkyl)(amino)carbene (CAAC) analogues of Thiele's hydrocarbon, a Kekulé diradical, and Schlenk's hydrocarbon, a non-Kekulé diradical, without using CAAC as a precursor. The CAAC analogue of Thiele's hydrocarbon has a singlet ground state, whereas the CAAC analogue of Schlenk's hydrocarbon contains two unpaired electrons. The latter forms a dimer, by an intermolecular double head-to-tail dimerization. This straightforward synthetic methodology is modular and can be extended for the generation of redox-active organic compounds.     

Exploiting Boron Coordination: B←N Bond Supports a [2+2] Photodimerization in the Solid State and Generation of a Diboron Bis‐Tweezer for Benzene/Thiophene Separation

B←N coordination supports a [2+2] photodimerization in the solid state. The bond is defined by an orthogonal interaction between stilbazole and a phenylboronic ester to enable a stereocontrolled and rapid photoreaction. The cyclobutane photoproduct affords a novel diboron bis‐tweezer adduct that is used to separate a mixture of benzene and thiophene upon crystallization.     

Total Synthesis of (−)‐Perezoperezone through an Intermolecular [5+2] Homodimerization of Hydroxy p‐Quinone

The first copper‐catalyzed intermolecular [5+2] homodimerization of hydroxy p‐quinone is presented, furnishing bicyclo[3.2.1]octadienone core structures in typically good yields and excellent diastereoselectivities. Applying this synthetic approach enables a concise nine‐step total synthesis of (?)‐perezoperezone from commercially available 3,5‐dimethoxytoluene.     

Bifunctional Small‐Molecule Ligands of K‐Ras Induce Its Association with Immunophilin Proteins

Here we report the design, synthesis, and characterization of bifunctional chemical ligands that induce the association of Ras with ubiquitously expressed immunophilin proteins such as FKBP12 and cyclophilin A. We show this approach is applicable to two distinct Ras ligand scaffolds, and that both the identity of the immunophilin ligand and the linker chemistry affect compound efficacy in biochemical and cellular contexts. These ligands bind to Ras in an immunophilin‐dependent fashion and mediate the formation of tripartite complexes of Ras, immunophilin, and the ligand. The recruitment of cyclophilin A to GTP‐bound Ras blocks its interaction with B‐Raf in biochemical assays. Our study demonstrates the feasibility of ligand‐induced association of Ras with intracellular proteins and suggests it as a promising therapeutic strategy for Ras‐driven cancers.     

Di‐tert‐butyldiphosphatetrahedran: Katalytische Synthese des freien Phosphaalkin‐Dimers

Die Tetrahedrane sind eine bisher nur wenig entwickelte Verbindungsklasse und insbesondere ist mit AsP₃ bisher nur ein einziges neutrales, heteroatomares Tetrahedran bekannt. Hier berichten wir über die Synthese eines neutralen, molekularen X₂Y₂‐Tetraeders (X, Y=p‐Blockelemente), der gleichzeitig das erste Beispiel des seit langem postulierten freien Phosphaalkindimers ist. Di‐tert‐butyldiphosphatetrahedran, (tBuCP)₂, lässt sich aus dem Monomer tBuCP in einer nickelkatalysierten Dimerisierungsreaktion unter Verwendung von [(NHC)Ni(CO)₃] (NHC=1,3‐Bis(2,4,6‐trimethylphenyl)imidazolin‐2‐yliden (IMes) bzw. 1,3‐Bis(2,6‐diisopropylphenyl)imidazolin‐2‐yliden (IPr)) als Katalysator darstellen. Die Einkristallröntgenstrukturanalyse eines Silber(I)‐komplexes bestätigt die tetraedrische Struktur. Der Einfluss des N‐heterocyclischen Carbenliganden auf die katalytische Reaktion wird diskutiert und auf Basis von synthetischen, kinetischen und quantenmechanischen Untersuchungen wird ein möglicher Bildungsmechanismus vorgestellt.     

Total Synthesis of Actinorhodin

The enantioselective total synthesis of actinorhodin ( 1 ) is described. The synthesis features 1) dual benzyne reactions en route to the monomer, 2) the trans‐selective installation of the side chain, and 3) a regioselective oxidative dimerization.