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We describe the regioselective prenylation of 3-bromocarbazole by palladium(0)-catalysed cross coupling with a prenylstannane or a prenylboronate. The procedure is applied to the synthesis of precursors for biologically active carbazole alkaloids.

We describe the first total synthesis of the recently discovered pyrano[3,2- a ]carbazole alkaloid clausenalansine A. The synthetic strategy for the construction of this formylpyrano[3,2- a ]carbazole is based on a sequence of Buchwald–Hartwig coupling, palladium(II)-catalyzed oxidative cyclization, Lewis acid promoted annulation of the pyran ring, and chemoselective oxidation of a methyl to a formyl group. [ABSTRACT FROM AUTHOR]

We describe a short and efficient synthetic route to euchrestifoline. Key steps of our approach are the iron(III)‐catalyzed Wacker‐type oxidation of a chromene derivative with hexadecafluorophthalocyanine‐iron (FePcF16) as catalyst, a palladium(0)‐catalyzed Buchwald–Hartwig amination, and the final palladium(II)‐catalyzed oxidative cyclization of the resulting diarylamine to the natural product. [ABSTRACT FROM AUTHOR]

We describe the first total synthesis of the pyrano[3,2-a]carbazole alkaloid 7-isovaleryloxy-8-methoxygirinimbine, using a palladium(II)-catalyzed double C-H-bond activation for construction of the carbazole framework and a phenylboronic acid catalyzed annulation of the pyran ring as key steps. [ABSTRACT FROM AUTHOR]

We describe the first total synthesis of the cytotoxic carbazole alkaloid excavatine-A. The carbazole framework was constructed through double C-H bond activation of a diarylamine by using our palladium(II)-catalyzed oxidative cyclization. Treatment of the intermediate 8-hydroxycarbazoles with prenal and different additives led either to pyrano[2,3-a]carbazoles or to [1,4]oxazepino[2,3,4-jk]carbazoles. The pyran annulation was investigated to determine the influence of substitution pattern, additives, and reaction time on the selectivity. [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]

A series of diphosphonate-bridged dipalladacycles [(phpy)Pd(EtO)P(O)], [(bhq)Pd(EtO)P(O)], [(phpz)Pd(EtO)P(O)] (phpy=2-phenylpyridine, bhq=benzo[h]quinoline, phpz=1-phenylpyrazole), which are known to be involved in catalytic C-H phosphonation reactions, was prepared and characterized by NMR spectroscopy and cyclic voltammetry in acetonitrile solutions and in carbon paste electrode. Diphosphonate dipalladacycles are oxidized irreversibly at more positive potentials as distinguished from related acetate palladacycles. Electrochemical preparative oxidations carried out under mild conditions without any specially added oxidants quantitatively afforded corresponding arylphosphonates. For complete conversion of dipalladacycles into arylphosphonates, four electrons per each palladium atom are required, that probably indicates a mechanism involving Pd(IV)/Pd(II) redox couple. [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 describe the synthesis of the naturally occurring 2,7-dioxygenated formylcarbazole alkaloids 7-methoxymukonal, 7-methoxy- O-methylmukonal, and the murrayalines A-C. The carbazole framework was constructed by a Buchwald-Hartwig amination and a subsequent palladium(II)-catalyzed oxidative cyclization. [ABSTRACT FROM AUTHOR]

Stufenökonomie: Aryl ‐ Pyran ‐ verknüpfte Biscarbazol ‐ Alkaloide der Murrafolingruppe (siehe Kristallstruktur von Murrafolin A; grau C, weiß H, blau N, rot O) wurden durch eine neuartige Dominoreaktion bestehend aus einer Sonogashira ‐ Kupplung, einer Claisen ‐ Umlagerung und einer Elektrocyclisierung erhalten. Der Ein ‐ Topf ‐ Prozess ermöglicht die einfache Synthese dieser strukturell anspruchsvollen Alkaloide in nur wenigen Schritten. [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 new family of sterically hindered alkyl(tri-tert-butyl) phosphonium salts (n-CnH2n+1 with n = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20) was synthesized and evaluated as stabilizers for the formation of palladium nanoparticles (PdNPs), and the prepared PdNPs, stabilized by a series of phosphonium salts, were applied as catalysts of the Suzuki cross-coupling reaction. All investigated phosphonium salts were found to be excellent stabilizers of metal nanoparticles of small catalytically active size with a narrow size distribution. In addition, palladium nanoparticles exhibited exceptional stability: the presence of phosphonium salts prevented agglomeration and precipitation during the catalytic reaction. [ABSTRACT FROM AUTHOR]

The tetracyclic pyrido[4,3-b]carbazole olivacine and four of its oxygenated derivatives have been synthesized by a late-stage palladium-catalyzed Heck-type cyclization of the pyrrole ring as a key step. In a test for the inhibition of the growth of Mycobacterium tuberculosis, 9-methoxyolivacine showed the most significant inhibitory activity against Mycobacterium tuberculosis, with an MIC90 value of 1.5 μM. [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]

The article presents chemical equations related to the article Palladium(II) Catalyzed Synthesis of the Formylcarbazole Alkaloids Murrayaline, Methoxymukonal, and 7-Methoxy-O-methylmukonal (IIb) by R. Hesse, and others, published in the periodical "European Journal of Organic Chemistry" in 2014.