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Dibenzoacridines were prepared by alkyne–carbonyl-metathesis and the optical properties of the products were studied.

Photocatalytic dehydrogenative [2 + 2] cycloadditions between amines and alkenes were developed that allow for the stereoselective and high-yielding synthesis of functionalized azetidines. The oxidative formal Aza Paternò-Büchi reactions are induced by photoredox-catalyzed aerobic oxidation of dihydroquinoxalinones

Lewis acid-catalysed oxa Diels–Alder reactions of unsaturated azepino[1,2-a]indole diones with enol ethers lead to tetracyclic azepane-fused pyrano[3,2-b]indoles, with high stereoselectivity and under mild reaction conditions.

Spirocyclic diindenothiophenes were prepared by cyclization of tosylhydrazones, readily available from ketones, with 3,4-dibromo-2,5-bis(2-bromphenyl)thiophene. For bicyclic ketones, the bis-spirocycles were formed with very good diastereoselectivity.

A new synthetic route to 1H-1,2,3-triazole-4,5-dithiols (tazdtH2) as ligands for the coordination of NiII, PdII, PtII and CoIII via the dithiolate unit is presented. Different N-protective groups were introduced with the corresponding azide via a click-like copper-catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC) and fully characterized by NMR spectroscopy. Possible isomers were isolated and an alternative synthetic route was investigated and discussed. After removal of the benzyl protective groups on sulfur by in situ-generated sodium naphthalide, complexes at the [(dppe)M] (M = Ni, Pd, Pt), [(PPh3)2Pt] and [(η5-C5H5)Co] moieties were prepared and structurally characterized by XRD analysis. In this process, the by-products 11 and 12 as monothiolate derivatives were isolated and structurally characterized as well. With regioselective coordination via the dithiolate unit, the electronic influence of different metals or protective groups at N was investigated and compared spectroscopically by means of UV/Vis spectroscopy and cyclic voltammetry. Complex [(η5-C5H5)Co(5c)] (10), is subject to a dimerization equilibrium, which was investigated by temperature-dependent NMR and UV/Vis spectroscopy (solution and solid-state). The thermodynamic parameters of the monomer/dimer equilibrium were derived.

Naphthothiophenes were prepared from commercially available 2,3-dibromothiophenes in two steps by one-pot Suzuki/Sonogashira or Sonogashira/Suzuki coupling reactions, followed by intramolecular alkyne-carbonyl-metathesis reactions. The final cyclization reaction proceeds in the presence of

Imidazo[1,2-a]benzoazepines were prepared in good yields by combination of Pd catalyzed cross coupling reactions with alkyne-carbonyl metathesis (ACM).

The tricyclic azepino[1,2-a]indole acetates 7, readily accessible by visible-light-driven catalytic photooxygenation of cyclohepta[b]indoles 1, are convenient precursors to novel and uncommon cyclic C,N-diacyliminium ions 3. We report here the first Lewis acid-catalyzed C-C bond forming reactions of these species with TMSCN and silyl enol ethers as nucleophiles and utilizing TIPSOTf as well as Sc(OTf)3 as catalysts. Employing Sc(OTf)3/pybox complexes as a chiral catalyst system, regio- and enantioselective asymmetric alkylations with silyl enol ethers were achieved.

Electrophilic aromatic substitution (EAS) can provide a straightforward approach to the efficient synthesis of functionalized complex aromatic molecules. In general, Lewis acids serve as a beneficial stimulus for the formation of a Wheland complex, the intermediate in the classical S

A concise and modular synthesis of pyrrolo[1,2-a][1,6]- and [1,8]naphthyridines by a one-pot two-step reaction consisting of electrophilic acylation followed by an alkyne-carbonyl-metathesis reaction as the final cyclization step is reported. This developed synthetic methodology allows the facile synthesis of these heterocyclic core structures in mainly high overall yields under metal-free conditions. Reaction conditions are carefully optimized and display a novel supplement to access these tricyclic heterocyclic compounds.

A variety of 4-methoxysalicylates and related polyketide-type phenols are regioselectively prepared by formal [3+3] cyclocondensations of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-oxo-orthoesters. Cycloalkyl-substituted salicylates were prepared for the first time.

We show that the carboxyl-functionalized ionic liquid 1-(carboxymethyl)pyridinium bis(trifluoromethylsulfonyl)imide [HOOC-CH

A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ‐η2‐C,C′‐κ2‐S,P‐C2(PPh2)S}Ru(η5‐C5H5)(PPh3)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side‐on carbon P,S‐chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like‐isomer is oxidized at W while the unlike‐isomer is oxidized at Ru, which is proven by IR, NIR and EPR‐spectroscopy supported by spectro‐electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ‐η2‐C,C′‐κ2‐S,P‐C2(PPh2)S}Ru(η5‐C5H5)‐(PPh3)], in which valence trapped WIII/RuII and WII/RuIII cationic species are at equilibrium., Diastereomers differ in physical properties: A case of real metal/metal redox isomerism is observed in a dinuclear complex with a particularly short bridging ligand. The two stereogenic complex moieties at W and Ru, respectively, are linked by an alkyne based phosphine thiolate chelate ligand. Oxidation of the like isomer pertains to tungsten, whereas the unlike isomer is oxidised at ruthenium. The diastereomers show opposite redox behaviour!

Attempts have been made to prepare salts with the labile tris(trimethylsilyl)chalconium ions, [(Me3Si)3E]+ (E=O, S), by reacting [Me3Si‐H‐SiMe3][B(C6F5)4] and Me3Si[CB] (CB−=carborate=[CHB11H5Cl6]−, [CHB11Cl11]−) with Me3Si‐E‐SiMe3. In the reaction of Me3Si‐O‐SiMe3 with [Me3Si‐H‐SiMe3][B(C6F5)4], a ligand exchange was observed in the [Me3Si‐H‐SiMe3]+ cation leading to the surprising formation of the persilylated [(Me3Si)2(Me2(H)Si)O]+ oxonium ion in a formal [Me2(H)Si]+ instead of the desired [Me3Si]+ transfer reaction. In contrast, the expected homoleptic persilylated [(Me3Si)3S]+ ion was formed and isolated as [B(C6F5)4]− and [CB]− salt, when Me3Si‐S‐SiMe3 was treated with either [Me3Si‐H‐SiMe3][B(C6F5)4] or Me3Si[CB]. However, the addition of Me3Si[CB] to Me3Si‐O‐SiMe3 unexpectedly led to the release of Me4Si with simultaneous formation of a cyclic dioxonium dication of the type [Me3Si‐μO‐SiMe2]2[CB]2 in an anion‐mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me3Si)3E]+ and [(Me3Si)2(Me2(H)Si)E]+ ion formation are presented as well as mechanistic investigations on the template‐driven transformation of the [(Me3Si)3E]+ ion into a cyclic dichalconium dication [Me3Si‐μE‐SiMe2]2 2+., Labile chalconium ions of the type [(Me3Si)3E]+ (E=O, S) were generated by reacting [Me3Si‐H‐SiMe3][B(C6F5)4] and Me3Si[CB] (CB−=carborate=[CHB11H5Cl6]−, [CHB11Cl11]−) with Me3Si‐E‐SiMe3. A ligand exchange in case of the oxonium species, leading to the surprising formation of the persilylated [(Me3Si)2(Me2(H)Si)O]+ oxonium ion, was observed. With Me3Si[CB] as silylating reagent, a cyclic dioxonium dication of the type [Me3Si‐μO‐SiMe2]2[CB]2 was isolated in an anion‐mediated reaction.

Formal coordination of phosphorus(III) by a calix[4]pyrrole Schiff base ligand was achieved through the reaction of this ligand with PCl3 under basic conditions. The reaction product adopts a Pacman conformation with two P-Cl moieties, one in exo and one in endo position. It represents the first non-metal compound of calix[4]pyrrole Schiff base ligands and of Pacman ligands in general. The spatial neighborhood of the two phosphorus atoms enables cooperative reactions. As a first example, the chloride abstraction with AgOTf is presented, yielding a macrocyclic dication with two embedded phosphorus(III) monocations, which both undergo a cooperative, internal activation reaction with an adjacent C=N double bond. This intramolecular redox process affords two pentacoordinated phosphorus(V) centers within the Pacman dication. All reaction products were fully characterized and all results are supported by computations.

Dibenzocycloheptanones (dibenzotropones) were prepared by Bronsted acid mediated intramolecular alkyne-carbonyl metathesis (ACM) reactions. The cyclization precursors are readily available by Sonogashira reaction of 2-bromobenzoyl chloride with terminal alkynes, followed by Suzuki reactions with benzaldehydes. The ACM reactions are highly modular and atom economic and allow for the construction of two regioisomeric series of dibenzotropones.

A metal‐free, photoinduced aerobic tandem amine dehydrogenation/Povarov cyclization/aromatization reaction between N‐aryl glycine esters and indoles leads to tetracyclic 11H‐indolo[3,2‐c]quinolines under mild conditions and with high yields. The reaction can be performed by using molecular iodine along with visible light, or by combining an organic photoredox catalyst with a halide anion. Mechanistic studies reveal that product formation occurs through a combination of radical‐mediated oxidation steps with an iminium ion or N‐haloiminium ion [4+2]‐cycloaddition, and the N‐heterocyclic products constitute new analogues of the antiplasmodial natural alkaloid isocryptolepine., All metal‐free: A photoinduced tandem amine dehydrogenation/Povarov cyclization/aromatization reaction leads to isocryptolepine analogues with high yields, by using molecular iodine under visible light, or by combining an organic photoredox catalyst with a halide anion (see scheme; PC=photocatalyst).

The reactivity of the four-membered NP3 ring system [RN(μ-PCl)2 PR] (R=Mes*=2,4,6-tri-tert-butylphenyl) towards Lewis acids, Lewis bases, and reducing agents was investigated. Comparisons with the literature-known, analogous cyclic compounds [ClP(μ-NR)]2 (R=Ter=2,6-dimesitylphenyl) and [ClP(μ-PR)]2 (R=Mes*) are drawn, to obtain a better systematic understanding of the reactivity of cyclic NP species. Apart from experimental results, DFT computations are discussed to further the insight into bonding and electronic structure of these compounds.

The synthesis of novel chromeno[2,3-c]pyrrol-9(2H)-ones via domino reaction of amino acids with aromatic α,β-ynones is described. Obtained chromeno[2,3-c]pyrrol-9(2H)-ones possess phosphatase inhibitory activity.

The Buchwald–Hartwig amination allows an efficient and convenient synthesis of biologically and pharmaceutically important acridones by formation of a six-membered ring. With the described method, a number of derivatives have been synthesized in up to 95% yield by using a variety of anilines as well as benzylic and aliphatic amines.

A facile synthesis and full characterization of a series of [Ag(arene)3][B(C6F5)4] salts (arene = C6H6, MeC6H5, EtC6H5, i-PrC6H5, n-PrC6H5, 1,2-Me2C6H4, 1,3-Me2C6H4, 1,4-Me2C6H4, 1,2,3-Me3C6H3, 1,2...

A straightforward, site-selective arylation of the bis(triflate) of estrone by Suzuki–Miyaura reactions has been developed. Monoarylation occurs selectively at the D-ring with good to excellent yield. Such products were exemplarily employed for the synthesis of estrones containing two different aryl substituents.

A series of 5,7,9-substituted 2-azapyrenes were synthesized for the first time. The synthesis relies on Brønsted acid promoted benzannulation of alkyne precursors prepared by palladium-catalyzed cross-coupling reactions. The synthetic strategy is efficient and the scope covers a variety of functional groups. The electrochemical behavior and photophysical properties of the products were investigated by UV-vis and fluorescence spectroscopy, cyclic voltammetry, and DFT calculations.

We report metal-free, photoinduced aerobic tandem dehydrogenative Povarov cyclisation/Csp3–H oxygenation reactions between N-aryl glycine esters and α-substituted styrenes, which efficiently lead to 4,4-disubstituted dihydroquinoline-3-ones under mild conditions. The reactions are mediated by iodine along with visible light irradiation, which allows for the in situ generation of the essential Bronsted acid HI, to catalyse the key imine [4+2]-cycloaddition.

Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side‐on λ5‐phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD‐DFT. Low‐temperature 31P NMR and EPR spectroscopic measurements combined with time‐dependent IR‐spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard‐modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations., A sought‐after combination of a phosphine as Lewis base and a carbenium centre as Lewis acid at a WII alkyne complex turned out to be stable as a diradical. Intramolecular cyclisation and subsequent deprotonation provided a side‐on complex of a λ5‐1‐phospha‐2,3‐didehydrofluoranthene, which can be denoted as λ5‐phosphinyne.

The reaction of TerN(SiMe3)BiCl2 (1) (Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl) with Lewis acids such as GaCl3 and Ag[OTf] (OTf = OSO2CF3) was studied. While the reaction of 1 with GaCl3 led to d...

4-Bromo-3-O-triflyl-estrone has been synthesized in 2 steps from estrone and was successfully employed in chemoselective palladium catalysed Suzuki-Miyaura reactions. Mono- and bis-arylations were carried out selectively by variation of ligands and solvents. Overall 19 derivatives of mono- and bis-arylated estrones were synthesized under optimized conditions in high yields. Various products showed atropisomerism which was studied in detail by NMR spectroscopy.

A new and efficient domino reaction of 3-chlorochromones with electron-rich aminoheterocycles was developed which allows for a convenient synthesis of a variety of pyrazolo[3,4-b]pyridines, pyrrolo[2,3-b]pyridines, pyrido[2,3-d]pyrimidines and benzofuro[3,2-b]pyridines. The products exhibit strong fluorescence. In addition, they exhibit significant ecto-5'-nucleotidase inhibition properties and cytotoxic behavior.

An efficient two-step palladium catalyzed synthesis of furo[3,2-b:4,5-b']diindoles, a hitherto unknown symmetrical heterocyclic core structure, was developed. The synthesis is based on a regioselective Suzuki-Miyaura cross coupling reaction of tetrabromofuran and subsequent double N-arylation. Selected compounds were studied with regard to their optical and electrochemical properties. The compounds show fluorescence with high quantum yields and non-reversible oxidation events. The compounds possess similar HOMO-LUMO band gaps compared to their sulfur and nitrogen analogs. Variation of the substituents hardly affects the HOMO-LUMO gap, but allows for some fine-tuning of the electron affinity and ionization potential as well as quantum yields. The compounds prepared represent interesting candidates for the development of organic electronic materials.