A short synthesis of koniamborine, a naturally occurring pyrano[3,2-b]indole

Clawson, Ronald W.; Söderberg, Björn C.G.

doi:10.1016/j.tetlet.2007.06.092

Cited by 27 publications

(10 citation statements)

References 14 publications

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“…Given the success of the synthesis of 3‐alkoxyindoles, the strategy was extended to the synthesis of the naturally occurring pyrano[3,2‐ b ]indole koniamborine (Scheme ) …”

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

“…[116] Given the success of the synthesis of 3-alkoxyindoles, the strategy was extended to the synthesis of the naturally occurring pyrano[3,2-b]indole koniamborine (Scheme 14). [117] The synthesis of 2-octadecyl,3-methoxyindole by the same catalytic system unexpectedly failed, but use of the Pd(OAc) 2 / Phen combination allowed the reaction to go to completion. [118] Attempts to transform the methoxy group into the hydroxy one, failed (Scheme 15).…”

Section: Synthesis Of Indolesmentioning

confidence: 99%

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Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

2019

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Nitroarenes are the entry point for the production of most nitrogen‐containing aromatic compounds. Thus, any transformation that leads directly from them to the final product allows saving one or more synthetic steps. This review deals with homogeneously catalyzed reactions leading to the formation of N‐heterocyclic compounds from nitroarenes or nitroalkenes in one pot. Reactions that lead to the intermediate formation of amines are not considered. Carbon monoxide is the most often employed reductant because it allows selective reactions, is cheap, and only produces CO2 as stoichiometric byproduct. However, the difficulty in handling pressurized CO has stimulated in recent years the development of CO‐surrogates, that is molecules able to liberate CO during the reaction. The use of phosphines and diols has also been developed in conjunction with molybdenum catalysts. The review focusses in more detail on the literature in the period 2006–2018, but reference to earlier work is made when necessary to put recent results in a more general context.

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“…Given the success of the synthesis of 3‐alkoxyindoles, the strategy was extended to the synthesis of the naturally occurring pyrano[3,2‐ b ]indole koniamborine (Scheme ) …”

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

Section: Synthesis Of Indolesmentioning

confidence: 99%

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

2019

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“…A γ-pyrone bearing substrate was also readily cyclized to give pyrano[3,2- b ]indole ( 26 ) in modest yield, which can be easily converted to the naturally occurring alkaloid koniamborine via N -methylation. 24 Biindole ( 27 ) could be prepared following mono-cyclization of ( E )-3-(2-nitrostyryl)-1 H -indole using our catalytic reaction conditions.…”

Section: Resultsmentioning

confidence: 99%

Biphilic Organophosphorus-Catalyzed Intramolecular C_sp²–H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations

et al. 2018

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A small-ring phosphacycloalkane (1,2,2,3,4,4-hexamethylphosphetane, 3) catalyzes intramolecular C–N bond forming heterocyclization of o-nitrobiaryl and –styrenyl derivatives in the presence of a hydrosilane terminal reductant. The method provides scalable access to diverse carbazole and indole compounds under operationally trivial homogeneous organocatalytic conditions, as demonstrated by 17 examples conducted on one-gram scale. In situ NMR reaction monitoring studies support a mechanism involving catalytic PIII/PV=O cycling, where tricoordinate phosphorus compound 3 represents the catalytic resting state. For the catalytic con-version of o-nitrobiphenyl to carbazole, the kinetic reaction order was determined for phosphetane catalyst 3 (first order), substrate (first order), and phenylsilane (zeroth order). For differentially 5-substituted 2-nitrobiphenyls, the transformation is accelerated by electron–withdrawing substituents (Hammett factor ρ = +1.5), consistent with the accrual of negative charge on the nitro substrate in the rate-determining step. DFT modeling of the turnover-limiting deoxygenation event implicates a rate-determining (3+1) cheletropic addition between the phosphetane catalyst 3 and 2-nitrobiphenyl substrate to form an unobserved pentacoordinate spiro-bicyclic dioxazaphosphetane, which decomposes via (2+2) cycloreversion giving one equivalent of phosphetane P-oxide 3•[O] and 2-nitrosobiphenyl. Experimental and computational investigations into the C–N bond forming event suggest the involvement of an oxazaphosphirane (2+1) adduct between 3 and 2-nitrosobiphenyl, which evolves through loss of phosphetane P-oxide 3•[O] to give the observed carbazole product via C–H insertion in a nitrene-like fashion.

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“…indol-9(1H)-yl}-ethanone was synthesized in good yield by heating N- (2-bromo-4-methylphenyl)-N-(4-methyl-3,6-dihydro-2H-pyran-3-yl)acetamide in boiling toluene in the presence of palladium(II) acetate, triphenylphosphine, copper(II) acetate, triethylamine, and potassium carbonate.Representatives of the pyranoindole series are few in number; nevertheless, some pyranoindole derivatives exhibit biological activity [1][2][3]. In the present work we tried to build up fused pyranoindole system by cyclization of a mixture of syn and anti atropisomers of N-(2-bromo-4-methylphenyl)-N-(4-methyl-3,6-dihydro-2H-pyran-3-yl)acetamide (IIa) under conditions of metal complex catalysis, which is widely used in the synthesis of nitrogen-containing heterocycles [4,5].…”

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confidence: 99%

Synthesis of 1-{4a,6-dimethyl-4a,9a-dihydropyrano-[3,4-b]indol-9(1H)-yl}ethanone

2012

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Heating of the bromination product of 4-methyl-3,6-dihydro-2H-pyran with 4-toluidine or 2-bromo-4-methylamiline in triethylamine gave 4-methyl-N-(4-methylphenyl)-and N-(2-bromo-4-methylphenyl)-4-methyl-3,6-dihydro-2H-pyran-3-amines which were converted into the corresponding amides by reaction with bromo-or chloroacetyl chloride. indol-9(1H)-yl}-ethanone was synthesized in good yield by heating N- (2-bromo-4-methylphenyl)-N-(4-methyl-3,6-dihydro-2H-pyran-3-yl)acetamide in boiling toluene in the presence of palladium(II) acetate, triphenylphosphine, copper(II) acetate, triethylamine, and potassium carbonate.Representatives of the pyranoindole series are few in number; nevertheless, some pyranoindole derivatives exhibit biological activity [1][2][3]. In the present work we tried to build up fused pyranoindole system by cyclization of a mixture of syn and anti atropisomers of N-(2-bromo-4-methylphenyl)-N-(4-methyl-3,6-dihydro-2H-pyran-3-yl)acetamide (IIa) under conditions of metal complex catalysis, which is widely used in the synthesis of nitrogen-containing heterocycles [4,5]. Compounds syn-IIa and anti-IIa were synthesized by reaction of acetyl bromide with N-pyranyl-substituted 2-bromo-4-methylaniline (I). The latter was prepared by reaction of 2-bromo-4-methylaniline [6] with the product of bromine addition to 4-methyl-3,6-dihydro-2H-pyran in carbon tetrachloride [7] (Scheme 1).The existence of compound IIa as two atropisomers was determined by spectral methods. Signals in the 1 H NMR spectra from the 3-H and 5-H protons in the pyran ring were assigned to particular atropisomers on the basis of published data [8]. According to the 1 H NMR data, the syn/anti ratio was 1 : 3. The minor syn atropisomer was characterized by a broadened singlet from 3-H at δ 4.72 ppm. The corresponding signal of the major anti isomer was observed in a weaker field (δ 5.37 ppm, br.s). The 5-H proton resonated as a broadened singlet at δ 5.47 (syn) or 5.64 ppm (anti). Likewise, by reaction of compound I with chloroacetyl chloride we obtained a mixture of syn and anti atropisomers IIb whose 1 H and 13 C NMR spectra also contained double sets of some signals. For comparison, amine III having no substituent in the ortho position of the aromatic ring was converted into compound IV, and its 1 H NMR spectrum showed the absence of atropisomerism.Heterocyclization of amide IIa using the system copper(II) acetate-palladium(II) acetate with addition of triphenylphosphine, triethylamine, and potassium carbonate gave dihydropyrano [3,4-b]indole (V) in good yield. The reaction is likely to involve initial formation of palladium intermediate A or B. Both structures do not contradict published data [8][9][10]. Elimination of PdHL 2 Br from palladium derivative D formed as a result of successive transformations yields pyranoindole V.The structure of compound V was determined on the basis of its elemental composition and spectral parameters. The mass spectrum of V contained the molecular ion peak with m/z 244 [M + H] + . Signals in the 1 H NMR spectru...

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A short synthesis of koniamborine, a naturally occurring pyrano[3,2-b]indole

Cited by 27 publications

References 14 publications

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Biphilic Organophosphorus-Catalyzed Intramolecular C_sp²–H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations

Synthesis of 1-{4a,6-dimethyl-4a,9a-dihydropyrano-[3,4-b]indol-9(1H)-yl}ethanone

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A short synthesis of koniamborine, a naturally occurring pyrano[3,2-b]indole

Cited by 27 publications

References 14 publications

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Biphilic Organophosphorus-Catalyzed Intramolecular Csp2–H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations

Synthesis of 1-{4a,6-dimethyl-4a,9a-dihydropyrano-[3,4-b]indol-9(1H)-yl}ethanone

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Biphilic Organophosphorus-Catalyzed Intramolecular C_sp²–H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations