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The iron(III)‐catalyzed oxidative coupling of diarylamines to 2,2′‐bis(arylamino)‐1,1′‐biaryls and subsequent twofold palladium(II)‐catalyzed oxidative cyclization provide a convergent synthetic route to 1,1′‐bicarbazoles. Screening a range of different palladium(II) salts led to palladium(II) acetate, pivalate, and hexafluoroacetylacetonate as the most efficient catalysts. Remarkably, the twofold palladium(II)‐catalyzed oxidative cyclization can also be performed under argon. The mechanism for the oxidative cyclization under an inert gas presumably involves regeneration of the catalytically active palladium(II) species by oxidative addition of pivalic acid. [ABSTRACT FROM AUTHOR]

We describe an iron‐catalyzed asymmetric oxidative C−C coupling of diarylamines which proceeds at room temperature with air as final oxidant. Using hexadecafluorophthalocyanine‐iron(II) as catalyst in the presence of catalytic amounts of an axially chiral biaryl phosphoric acid, the resulting chiral 2,2′‐diamino‐1,1′‐biaryls are obtained in up to 90 % ee as confirmed by chiral HPLC. A detailed mechanism has been proposed with a radical cation‐chiral phosphate ion pair as key intermediate leading to the observed asymmetric induction. [ABSTRACT FROM AUTHOR]

We describe the oxygenation of tertiary arylamines, and the amination of tertiary arylamines and phenols. The key step of these coupling reactions is an iron‐catalyzed oxidative C−O or C−N bond formation which generally provides the corresponding products in high yields and with excellent regioselectivity. The transformations are accomplished using hexadecafluorophthalocyanine−iron(II) (FePcF16) as catalyst in the presence of an acid or a base additive and require only ambient air as sole oxidant. [ABSTRACT FROM AUTHOR]

The hexadecafluorophthalocyanine–iron complex FePcF16 was recently shown to convert olefins into ketones in the presence of stoichiometric amounts of triethylsilane in ethanol at room temperature under an oxygen atmosphere. Herein, we describe an extensive mechanistic investigation for the conversion of 2‐vinylnaphthalene into 2‐acetylnaphthalene as model reaction. A variety of studies including deuterium‐ and 18O2‐labeling experiments, ESI‐MS, and 57Fe Mössbauer spectroscopy were performed to identify the intermediates involved in the catalytic cycle of the oxidation process. Finally, a detailed and well‐supported reaction mechanism for the FePcF16‐catalyzed Wacker‐type oxidation is proposed. [ABSTRACT FROM AUTHOR]

A mild procedure for the oxidative C−C cross‐coupling of tertiary anilines with phenols is described which provides the products generally in high yields and with excellent selectivity. The reaction is catalyzed by the hexadecafluorinated iron–phthalocyanine complex FePcF16 in the presence of substoichiometric amounts of methanesulfonic acid and ambient air as sole oxidant. [ABSTRACT FROM AUTHOR]

Dibenzo[cde,opq]rubicene has been synthesized by an eight‐step reaction sequence including an iron‐mediated [2+2+1] cycloaddition and a flash vacuum pyrolysis as key steps. Two crystal modifications of the S‐shaped, planar polycyclic aromatic hydrocarbon have been obtained and characterized by X‐ray diffractometry. [ABSTRACT FROM AUTHOR]

Abstract: We describe the synthesis of 1,1′‐ and 2,2′‐bicarbazoles by oxidative homocoupling of 2‐ and 1‐hydroxycarbazoles. The oxidative coupling using catalytic amounts of F16PcFe can be applied to both groups of substrates. Although F16PcFe generally provides the best yields for the synthesis of 1,1′‐bicarbazoles, di‐tert‐butyl peroxide affords better results for the 2,2′‐bicarbazoles. In our study, we have achieved the first syntheses of the biscarbalexines A–C, bisglybomine B, 2,2′‐dihydroxy‐7,7′‐dimethoxy‐3,3′‐dimethyl‐1,1′‐bicarbazole, bispyrayafoline C, and bisisomahanine. The iron‐catalyzed coupling of koenigine led to an improved synthesis of 8,8′′‐biskoenigine and afforded an unprecedented decacylic product. Oxidative coupling of 1‐hydroxycarbazoles led to bisclausenol, and to the first total syntheses of bismurrayafoline B and D. [ABSTRACT FROM AUTHOR]

We have developed a short and simple synthesis of tetranuclear palladium(II) complexes that have been structurally confirmed by X-ray analysis. These complexes were formed in about 30 % overall yield by spontaneous metalation of dimethylaminoarene derivatives and exhibit a high stability. We have studied the utility of the tetranuclear palladium(II) complexes as precatalysts for Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions. Our novel complexes show excellent catalytic activities with high turnover numbers (TON) and high turnover frequencies (TOF) (e.g., for the Suzuki-Miyaura reaction: TON up to 538000 and TOF up to 23400 h−1 at room temperature). [ABSTRACT FROM AUTHOR]

The diverse mechanisms for the reductive elimination of biaryl compounds from diarylpalladium(II) complexes with a tetradentate ligand were investigated through a combined experimental and computational study. At least four distinct chemical triggers with specific regioselectivity exist for this elimination. Heating of the complexes in inert solvents (e.g., para-xylene) reveals their relatively high thermal stability as reflected by a very high barrier for a unimolecular reductive elimination. In contrast, electron-donor ligands like triphenylphosphine induce a facile reductive elimination via twofold associative ligand exchange as confirmed by kinetic experiments, which are in good agreement with the computational results. Oxidants, such as H2O2, can trigger an oxidation-induced reductive elimination via palladium(IV) intermediates at room temperature. Rearrangement of the diarylpalladium(II) complexes can occur in organic acids, facilitating a reductive elimination with distinct regiochemical outcome. [ABSTRACT FROM AUTHOR]

We describe a regioselective synthesis of 4- or 5-substituted carbazoles by oxidative cyclisation of meta-oxygen-substituted N-phenylanilines. Using the regiodirecting effect of a pivaloyloxy group, we prepared 4-hydroxycarbazole, a precursor for the enantiospecific synthesis of the β-adrenoreceptor antagonists (−)-( S)-carazolol ( 5) and (−)-( S)-carvedilol ( 6). Regioselective palladium(II)-catalysed cyclisation of different diarylamines led to total synthesis of glycoborine ( 7) and the first total syntheses of the phytoalexin carbalexin A ( 8), glybomine A ( 9) and glybomine B ( 10). For glybomine B ( 10), a 5-hydroxycarbazole was converted into the corresponding triflate and utilized for introduction of a prenyl substituent. [ABSTRACT FROM AUTHOR]

The synthesis of diarylpalladium(II) complexes by twofold aryl C−H bond activation was developed. These intermediates of oxidative cyclization reactions are stabilized by chelation with acetyl groups while still maintaining sufficient reactivity to study their reductive elimination. Four distinct triggers were found for the reductive elimination of these complexes to dibenzofurans and carbazoles. Thermal elimination occurs at very high temperatures, whereas ligand-promoted and oxidatively induced reductive eliminations proceed readily at room temperature. Under these conditions, no isomerization occurs. In contrast, weak Brønsted acids, such as acetic acid, lead to a sequence of proto-demetalation, isomerization to a κ3-diarylpalladium(II) complex, and reductive elimination to non-symmetrical cyclization products. [ABSTRACT FROM AUTHOR]

In addition to the prototypic amyloid-β (Aβ) peptides Aβ1-40 and Aβ1-42, several Aβ variants differing in their amino and carboxy termini have been described. Synthetic availability of an Aβ variant is often the key to study its role under physiological or pathological conditions. Herein, we report a protocol for the efficient solid-phase peptide synthesis of the N-terminally elongated Aβ-peptides Aβ−3-38, Aβ−3-40, and Aβ−3-42. Biophysical characterization by NMR spectroscopy, CD spectroscopy, an aggregation assay, and electron microscopy revealed that all three peptides were prone to aggregation into amyloid fibrils. Immunoprecipitation, followed by mass spectrometry, indicated that Aβ−3-38 and Aβ−3-40 are generated by transfected cells even in the presence of a tripartite β-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor. The elongated Aβ peptides starting at Val(−3) can be separated from N-terminally-truncated Aβ forms by high-resolution isoelectric-focusing techniques, despite virtually identical isoelectric points. The synthetic Aβ variants and the methods presented here are providing tools to advance our understanding of the potential roles of N-terminally elongated Aβ variants in Alzheimer's disease. [ABSTRACT FROM AUTHOR]

We describe the total synthesis of methylene-bridged biscarbazole alkaloids by using a late-stage Ullmann-type coupling of fully functionalised carbazole subunits. The carbazole derivatives were synthesised via a sequence of palladium(0)- and palladium(II)-catalysed coupling reactions. Our approach has provided bismurrayafoline-A, bismurrayafolinol, chrestifolines B-D, and the first total synthesis of murrastifoline-C and murrafoline-E. [ABSTRACT FROM AUTHOR]

The DIBAL-H promoted reductive pyran ring opening of dialkylpyrano[3,2- a]carbazoles provides a direct access to a broad range of prenyl- and geranyl-substituted carbazoles. Formation of a pyran ring followed by reductive ring opening represents a new method for the introduction of prenyl and geranyl groups. In the course of the present work, we achieved the first total syntheses of the following eight carbazole alkaloids: clauraila-E, 7-hydroxyheptaphylline, 7-methoxyheptaphylline, mukoenine-B (clausenatine-A), mukoenine-A (girinimbilol), mahanimbinol (mahanimbilol), euchrestine-A, and isomurrayafoline-B. [ABSTRACT FROM AUTHOR]

The boronic acid-catalyzed annulation of citral opens up a short route to oxygenated cyclized monoterpenoid pyranocarbazole alkaloids. Thus, murrayamine-D is available in only three steps and 55% overall yield from the corresponding carbazole precursor. [ABSTRACT FROM AUTHOR]

We have developed a highly efficient route to 2-hydroxy-3-methylcarbazole ( 1) via a palladium-catalyzed construction of the carbazole skeleton. Using 1 as relay compound, different methods for annulations of pyran rings by reaction with terpenoid building blocks have been tested. The Lewis acid promoted reaction of 1 with prenal ( 21) opened up an efficient route to girinimbine ( 3) and the corresponding reaction with citral ( 25) afforded mahanimbine ( 5). Oxidation of compounds 3 and 5 provided murrayacine ( 4) and murrayacinine ( 6). Following the biogenetic proposal, mahanimbine ( 5) has been exploited for efficient biomimetic syntheses of the cyclized monoterpenoid pyrano[3,2- a]carbazole alkaloids cyclomahanimbine ( 7), mahanimbidine ( 8) and bicyclomahanimbine ( 9). The interconversions of 5, 7, 8 and 9 are described and mechanistic implications are discussed. Structural assignments are unambiguously verified by X-ray crystal structure determinations. Moreover, cyclomahanimbine ( 7) was transformed into murrayazolinine ( 10) and exozoline ( 11). [ABSTRACT FROM AUTHOR]

A space filling model of the X‐ray structure of the pyrano[3,2‐a]carbazole alkaloid mupamine is shown. Its synthesis, which involves the boronic acid‐catalyzed annulation of citral, is described in the Communication by H.‐J. Knölker et al. on page 8536 ff. [ABSTRACT FROM AUTHOR]