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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]

Clausenal (1,8‐dimethoxycarbazole‐3‐carbaldehyde) represents the only known naturally occurring 1,8‐dioxygenated carbazole alkaloid. However, the structural assignment for clausenal has recently been questioned because of some discrepancies between a synthetic sample and the natural product with respect to NMR data and melting points. Therefore, we have synthesized clausenal as well as two potential structural alternatives (1,5‐dimethoxycarbazole‐3‐carbaldehyde and 2,5‐dimethoxycarbazole‐3‐carbaldehyde) and compared their spectroscopic data with those reported for the isolated natural product. In conclusion from our investigation, we assume that the original structural assignment reported for clausenal most likely is correct. [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]

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 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 the total synthesis of murrayafoline-B and seven carbazole-1,4-quinone alkaloids. A palladium(II)-catalyzed oxidative cyclization is used to construct the carbazole skeleton. Pyran annulation and oxidation provide pyrayaquinone-A, -B, and -C. DIBAL-H-promoted reductive ring opening of pyrano[3,2-a]carbazole precursors leads to the prenylated and geranylated carbazole-1,4-quinone alkaloids murrayaquinone-B, -C, -D, and -E and to murrayafoline-B. [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]

Using the palladium(II)-catalyzed oxidative cyclization of a diarylamine and the annulation of a dimethylpyran ring by Lewis acid promoted reaction with prenal as key steps, the total syntheses of the 6-oxygenated pyrano[3,2-a]carbazole alkaloids koenine and koenimbine, and of the 6,7-dioxygenated pyrano[3,2-a]carbazole alkaloids koenigine and koenigicine (koenimbidine, koenidine) were achieved. Moreover, these studies led to an improved synthetic route to the 2,6-dioxygenated carbazole alkaloid glycozolidol. Mukonicine, originally published as 6,8-dimethoxypyrano[3,2-a]carbazole, was found to be identical with koenigicine. [ABSTRACT FROM AUTHOR]

We describe a convergent route to 5,11-dihydroindolo[3,2-b]carbazoles using a twofold oxidative cyclization as key step. The method has been applied to the synthesis of a precursor for malasseziazole A and to the first total synthesis of malasseziazole C. [ABSTRACT FROM AUTHOR]

Using a palladium(II)-catalyzed oxidative cyclization of an N,N-diarylamine, we have achieved the total synthesis of the 2,8-dioxygenated carbazole alkaloids carbalexin B, clausine A, clauszoline M, and 2,8-dihydroxy-3-methylcarbazole. [ABSTRACT FROM AUTHOR]

A Buchwald-Hartwig amination and palladium(II)-catalyzed oxidative cyclization reaction sequence provided efficient access to a series of oxygenated tricyclic carbazoles. In the present work, this approach was applied to the total syntheses of the naturally occurring carbazole alkaloids 2-hydroxy-7-methylcarbazole, glycozolicine, mukoline, mukolidine, sansoakamine, glycozolidine, clausine-H (clauszoline-C), clausine-K (clauszoline-J), and methyl 2-hydroxy-7-methoxycarbazole-3-carboxylate, which was originally proposed as the structure of clausine-TY. The synthesis of the latter led to the structural reassignment of clausine-TY. [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 report the first total synthesis of murrastifoline B and an improved route to murrastifoline F using a twofold palladiumcatalyzed Buchwald-Hartwig amination as key step. The monomeric carbazole and the biaryl precursor are also prepared via palladium-catalyzed coupling reactions. [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]

Abstract: Using a palladium(II)-catalysed oxidative cyclisation as key step, we describe a highly efficient total synthesis of a series of naturally occurring 1,6-dioxygenated carbazole alkaloids: clausenine, 6-methoxymurrayanine, clausenol, clausine G, clausine I, clausine Z and methyl 1,6-dihydroxy-9H-carbazole-3-carboxylate. [Copyright &y& Elsevier]

Consecutive palladium-catalyzed C-N and C-C bond formation provides an efficient route to the 1,7,8-trioxygenated carbazole alkaloid murrayastine. [ABSTRACT FROM AUTHOR]

Using an iron-mediated construction of the carbazole framework, the first synthesis of streptoverticillin is described and the absolute configuration of the natural product is confirmed. The synthesis exploits a novel oxygen-mediated aromatization of tricarbonyliron-coordinated dihydrocarbazoles. Moreover, non-natural (R)-streptoverticillin is prepared for comparison. [ABSTRACT FROM AUTHOR]

The oxidative cyclization of 5-(2-amino-5-methoxycarbonylphenyl)-substituted tricarbonyl[η4-cyclohexa-1,3-diene]iron complexes by air in protic medium provides the corresponding tricarbonyl[η4-4a,9a-dihydro-9H-carbazole]iron complexes. This procedure is applied to the total synthesis of the 3-methoxycarbonylcarbazole alkaloids mukonine and mukonidine. [Copyright &y& Elsevier]

Focuses on the isolation and synthesis of biologically active carbazole alkaloids. Iron-mediated synthesis of carbazoles; Fischer indolization of phenylhydrazones; Thermal cyclization of 2-methyl-3-vinylindole.

Abstract: Using a palladium(II)-catalyzed oxidative cyclization and a regioselective nickel-mediated prenylation as key steps, the first total synthesis of the 1-oxygenated carbazole alkaloid ekeberginine has been achieved in six steps and in 63% overall yield. [Copyright &y& Elsevier]

The sequence of palladium(0)-catalyzed amination and palladium(II)-catalyzed oxidative formation of the biaryl bond provides a direct route to the 1,7-dioxygenated tricyclic carbazole alkaloids clausine Q and clausine R. [ABSTRACT FROM AUTHOR]

The first synthesis of the whole antiostatin family is described by using an iron-mediated carbazole synthesis, regioselective nitration at C-4 and establishing 5-isobutyl-1-nitrobiuret as a reagent for introduction of the antiostatin B side chain at C-4. [ABSTRACT FROM AUTHOR]

Highly convergent syntheses of substituted carbazoles are most conveniently achieved using organometallic chemistry. Construction of the carbazole framework via the iron-mediated route proceeds by a sequence of C-C and C-N bond formation. In the highly efficient palladium-catalyzed route the C-N bond is formed first followed by generation of the C-C bond. This article highlights some recent developments and applications to the total synthesis of biologically active carbazole alkaloids. [ABSTRACT FROM AUTHOR]

The palladium-catalyzed construction of the carbazole framework provides an efficient access to 3-hydroxy-6-methylcarbazole (glycozolinine) ( 5 ). Regioselective annulation of a pyran ring at glycozolinine ( 5 ) using either a C 5 - or a C 10 -building block leads to the pyrano[2,3- c ]carbazole alkaloids glycomaurin (5,6-pyranoglycozoline, eustifoline-A) ( 2 ) and eustifoline-B ( 4 ), respectively. Reductive opening of the pyran ring with DIBAL-H in the presence of an additional Lewis acid transformed 2 into the 5-prenyl-substituted carbazole alkaloid glycomaurrol ( 1 ) and 4 into the 5-geranyl-substituted homologue eustifoline-C ( 3 ). [ABSTRACT FROM AUTHOR]

We describe efficient synthetic routes to murrayamine A (mukoenine C), O-methylmurrayamine A, mahanine, O-methylmahanine, and murrayamine D and the first total syntheses of murrayamine E, I, and K. Key steps are a palladium-catalyzed construction of the carbazole framework and an annulation of the pyran ring, which is either catalyzed by phenylboronic acid or promoted by a Lewis acid. [ABSTRACT FROM AUTHOR]