Borane-Induced Dimerization of Arylallenes.

A series of arylallenes react with HB(C F ) in a 2:1 molar ratio to give the tail-to-tail 1,6-diaryl-2-boryl-hexa-1,5-diene coupling products. The reaction of the phenylallene substrate with HB(C F ) was shown to initially give the 2-boryl-3,4-diphenyl-1,5-hexadiene head-to-head coupling product which then rearranged, by a thermally induced Cope rearrangement, into the final product.

Non-Directed Cross-Dehydrogenative (Hetero)arylation of Allylic C(sp )-H bonds enabled by C-H Activation.

Herein, we report the selective, non-directed and cross-dehydrogenative coupling of allylic C(sp )-H bonds with C(sp )-H bonds of (hetero)arenes. The methodology employs olefins and (hetero)arenes which are abundantly available chemical feedstocks, and could be applied in late-stage functionalization reactions of pharmaceuticals. Furthermore, the system exclusively delivers the allylic C-C coupling products highlighting the preservation of the olefin substitution pattern for further derivatization.

Ferro- or antiferromagnetism? Heisenberg chains in the crystal structures of verdazyl radicals.

In this study, we address the question of the origin of ferromagnetic or antiferromagnetic interactions in alkynyl-substituted 1,5-diphenyl-6-oxo verdazyl radicals. While a TMS-alkynyl derivative (3) shows antiferromagnetic ordering at low temperatures, the corresponding deprotected alkynyl verdazyl (4) shows ferromagnetic interactions. For both compounds, magnetic Heisenberg chains are characteristic, which were studied systematically by means of X-ray crystallography and quantum chemical calculations.

Synthesis of new fluorinated proline analogues from polyfluoroalkyl β-ketoacetals and ethyl isocyanoacetate.

The reaction of trifluoroaldol acetal and other polyfluoroalkyl β-ketoacetals with ethyl isocyanoacetate was applied for the preparation of hitherto unknown fluorinated amino acids, cis- and trans-3-CF3/C2F5-prolines as well as trans-3-CF2Br/CF2Cl/CHF2-3-hydroxyprolines.

Natural Product-Based 1,2,3-Triazole/Sulfonate Analogues as Potential Chemotherapeutic Agents for Bacterial Infections.

Despite the vast availability of antibiotics, bacterial infections remain a leading cause of death worldwide. In an effort to enhance the armamentarium against resistant bacterial strains, 1,2,3-triazole () and sulfonate () analogues of natural bioactive precursors were designed and synthesized. Preliminary screening against two Gram-positive ( and ) and four Gram-negative bacterial strains (, , , and ) was performed to assess the potency of these analogues as antibacterial agents.

Formation of borata-alkene/iminium zwitterions by ynamine hydroboration.

The ynamine TMP-C[triple bond, length as m-dash]C-CH3 adds HB(C6F5)2 to give the unsaturated C2-bridged N/B FLP 5. Compound 5 shows the structural data indicating a marked participation of the zwitterionic mesomeric borata-alkene/iminium form. It splits dihydrogen at r.

Oxygen-Insensitive Aggregates of Pt(II) Complexes as Phosphorescent Labels of Proteins with Luminescence Lifetime-Based Readouts.

The synthesis and photophysical properties of a tailored Pt(II) complex are presented. The phosphorescence of its monomeric species in homogeneous solutions is quenched by interaction with the solvent and therefore absent even upon deoxygenation. However, aggregation-induced shielding from the environment and suppression of rotovibrational degrees of freedom trigger a phosphorescence turn-on that is not suppressed by molecular oxygen, despite possessing an excited-state lifetime ranging in the microsecond scale.

Fluorocyclisation via I(I)/I(III) catalysis: a concise route to fluorinated oxazolines.

Herein, we describe a catalytic fluorooxygenation of readily accessible -allylcarboxamides via an I(I)/I(III) manifold to generate 2-oxazolines containing a fluoromethyl group. Catalysis is conditional on the oxidation competence of Selectfluor, whilst HF serves as both a fluoride source and Brønsted acid activator. The C(sp)-F bond of the mono-fluoromethyl unit and the C(sp)-O bond of the ring are aligned in a relationship thereby engaging in stabilising hyperconjugative interactions with , electron-rich σ-bonds (σ→σ* and σ→σ*).

Toward Tunable Electroluminescent Devices by Correlating Function and Submolecular Structure in 3D Crystals, 2D-Confined Monolayers, and Dimers.

The synthesis of new Pt(II) complexes bearing tailored cyclometalated C^N*N^C luminophores is reported along with their photophysical properties. The emission of the monomeric species can be blue shifted upon formal isosteric replacement of two C-H units by N atoms at the two cyclometalating rings. Their remarkable stability upon sublimation was demonstrated by means of scanning tunneling microscopy, which also revealed a defined self-assembly behavior leading to supramolecular arrays, showing a 3-fold symmetry in 2D-confined monolayers.

Monomeric Fe(iii) half-sandwich complexes [Cp'FeX] - synthesis, properties and electronic structure.

The half-sandwich complex [Cp'Fe(μ-I)] (1; Cp' = η-1,2,4-(MeC)CH) is cleaved when heated in toluene to form a cation-anion pair [{Cp'Fe(η-toluene)}{Cp'FeI}] (2), in which the two Fe(ii) atoms adopt different spin states, i.e., a low-spin (S = 0) and a high-spin (S = 2) configuration.

Solid state frustrated Lewis pair chemistry.

In solution the PCy/B(CF) pair is rapidly deactivated by nucleophilic aromatic substitution. In the solid state deactivation is effectively suppressed and the active frustrated phosphane/borane Lewis pair splits dihydrogen or adds to sulfur dioxide. A variety of phosphane/B(CF) pairs have been used to carry out active FLP reactions in the solid state.

Ligand-Enabled Enantioselective Csp3 -H Activation of Tetrahydroquinolines and Saturated Aza-Heterocycles by Rh.

The first rhodium(I)-catalyzed enantioselective intermolecular Csp3 -H activation of various saturated aza-heterocycles including tetrahydroquinolines, piperidines, piperazines, azetidines, pyrrolidines, and azepanes is presented. The combination of a rhodium(I) precatalyst and a chiral monodentate phosphonite ligand is shown to be a powerful catalytic system to access a variety of important enantio-enriched heterocycles from simple starting materials. Notably, the Csp3 -H activation of tetrahydroquinolines is especially challenging due to the adjacent Csp2 -H bond.

Selective formation of heterocyclic trans-cycloalkenes by alkyne addition to a biphenylene-based phosphane/borane frustrated Lewis pair.

The intramolecular 1-PMes2/8-B(C6F5)2 substituted biphenylene frustrated Lewis pair 4 shows some behavior reminiscent of intermolecular FLP systems. It undergoes trans-1,2-addition to a series of 1-alkynes to give the respective heterocyclic eight-membered E-alkenes 8. The P/B FLP 4 also reacts with triplet dioxygen to yield the [P]-O-[B](OC6F5) containing oxygenation product.

Zirconocene mediated acetylboron chemistry.

The methyl zirconocene complex Cp*2Zr(Me)OMes reacts with H3C-B(C6F5)2 and CO to give the respective acetyl(methyl)borate Zr complex. Cp*2Zr(H)OMes reacts with H3C-B(C6F5)2 and CO to give the respective acetyl(hydrido)borate Zr product, admixed with a minor amount of the formyl(methyl)borate Zr complex isomer. Prolonged exposure to CO under close to ambient conditions results in the uptake of another CO equivalent to yield the corresponding borata-β-lactone zirconocene product.

Metal-Free Acetylene Coupling by the (C F ) B-X 1,2-Halogenoboration Reaction.

(C F ) B-halides were conveniently prepared by treatment of (C F ) BH with tritylchloride or -bromide, respectively. With cyclopropylacetylene, (C F ) BBr underwent sequential cis-1,2-halogenoboration followed by 1,2-carboboration to give the 4-bromo-2,4-dicyclopropylbutadienyl-B(C F ) product. It reacted further with additional cyclopropylacetylene to give the linear triene and tetraene products in a metal-free alkyne oligomerization reaction.

Formation of macrocyclic ring systems by carbonylation of trifunctional P/B/B frustrated Lewis pairs.

The trifunctional P/B/B frustrated Lewis pairs featuring bulky aryl groups at phosphorus [Dmesp (), Tipp (), Mes* ()] react with H by heterolytic hydrogen splitting followed by cleavage of HB(CF) to give the zwitterionic six-membered heterocyclic PH phosphonium/borate products . Compounds react with carbon monoxide by means of a Lewis acid induced CO insertion/rearrangement sequence that eventually results in the formation of the macrocyclic dimers . The respective carbonylation reaction of the Mes*P/B/B FLP gives the macrocyclic trimer .

Formation and reactions of active five-membered phosphane/borane frustrated Lewis pair ring systems.

The reactive five-membered frustrated P/B Lewis pair 6a was generated from Tipp-P(vinyl)2 (Tipp: 2,4,6-triisopropylphenyl) by a series of anti-Markovnikov and Markovnikov hydroboration reactions. The in situ generated compound dimerized to give 7a under kinetic control and the dimer pair 8a/9a under thermodynamic control. The Mes*-P(vinyl)2 analogue (Mes*: 2,4,6-tri-tert-butylphenyl) reacts in a similar way, but in this case the thermodynamic dimers are observed at r.

Synthesis of 3-aza[4.4.3]propellanes with high σ receptor affinity.

In order to obtain rigid σ receptor ligands with defined orientation of pharmacophoric elements, the azapropellane scaffold was chosen. Schmidt rearrangement of propellan-8-ones 6 and 10 provided 3-azapropellan-4-ones 7 and 11. Benzylation of the secondary lactams 7 and 11 followed by LiAlH reduction furnished the azapropellanes 4a and 4c, respectively.

Highly Enantioselective [5 + 2] Annulations through Cooperative N-Heterocyclic Carbene (NHC) Organocatalysis and Palladium Catalysis.

The highly enantioselective [5 + 2] annulation of enals with vinylethylene carbonates through a cooperative N-heterocyclic carbene (NHC)/Pd catalytic system is reported. The use of a bidentate phosphine ligand was crucial to prevent coordination of the NHC organocatalyst to the active Pd catalyst. The complementary and matched combination of the chiral NHC catalyst and chiral phosphine ligand promotes high levels of both reactivity and enantioselectivity (mostly ≥99% ee).

Unprecedented Dearomatized Spirocyclopropane in a Sequential Rhodium(III)-Catalyzed C-H Activation and Rearrangement Reaction.

An unprecedented dearomatized spirocyclopropane intermediate was discovered in a sequential Cp*Rh -catalyzed C-H activation and Wagner-Meerwein-type rearrangement reaction. How the oxidative O-N bond is cleaved and the role of HOAc were uncovered in this study. Furthermore, a Cp*Rh -catalyzed dearomatization reaction of N-(naphthalen-1-yloxy)acetamide with strained olefins was developed, affording a variety of spirocyclopropanes.

Lewis Acid Catalyzed Stereoselective Dearomative Coupling of Indolylboron Ate Complexes with Donor-Acceptor Cyclopropanes and Alkyl Halides.

Indolylboron ate complexes readily generated from 2-lithioindoles and boronic esters underwent multicomponent dearomative coupling with D-A cyclopropanes and alkyl halides in the presence of Sc(OTf) as a catalyst. The reactions proceeded with complete diastereoselectivity and excellent stereospecificity to provide indolines containing three contiguous stereocenters. The valuable boronic ester moiety remains in the product and allows for subsequent functionalization.

Palladium-Catalyzed Decarboxylative Heck-Type Coupling of Activated Aliphatic Carboxylic Acids Enabled by Visible Light.

The palladium-catalyzed coupling reaction of N-hydroxyphthalimide esters and styrenes to deliver exclusively (E)-substituted olefins under irradiation with visible light is reported. This method tolerates N-hydroxyphthalimide esters derived from primary, secondary, tertiary as well as benzylic carboxylic acids. Notably, Pd(PPh ) is employed as an inexpensive palladium source and no addition of base or classical photocatalyst is required.

Formation of Reactive π-Conjugated Frustrated N/B Pairs by Borane-Induced Propargyl Amine Rearrangement.

N-Propargyltetramethylpiperidine reacts with a series of trans-alkenyl-B(CF) compounds to give the substituted alkenyl-bridged frustrated N/B Lewis pairs 5. Their structures and spectroscopic features indicate a pronounced participation of the mesomeric s-trans-iminium/borata-alkene resonance form. The compounds are thought to be formed in a stepwise addition/rearrangement process which is initiated by a trans-1,2-amine/borane FLP addition to the carbon-carbon triple bond to generate a reactive zwitterionic aziridinium/alkenylborate intermediate.

Large-scale total synthesis of C-labeled citrinin and its metabolite dihydrocitrinone.

The analysis of the nephrotoxic mycotoxin citrinin in food, feed, and physiological samples is still challenging. Nowadays, liquid chromatography coupled with mass spectrometry is the method of choice for achieving low limits of detection. But matrix effects can present impairments for this method.

Enantioselective Synthesis of the Spirotropanyl Oxindole Scaffold through Bimetallic Relay Catalysis.

Spirotropanyl oxindole alkaloids like alstonisine and chitosenine show a wide range of bioactivites. We report the first enantioselective synthesis of the spirotropanyl oxindole scaffold by means of a bimetallic relay catalysis strategy. A new class of E-oximino α-diazo ketones was developed for the intramolecular generation of transient azomethine ylides catalyzed by an achiral Rh complex and a subsequent intermolecular 1,3-dipolar cycloaddition catalyzed by a chiral N,N'-dioxide Nd Lewis acid complex.