Nitrogen‐Containing Tricyclic and Tetracyclic Compounds by Stereoselective Samarium Diiodide Promoted Cyclizations of Quinolyl‐Substituted Ketones – A New Access to Azasteroids

Aulenta, Francesca; Wefelscheid, Ulrike K.; Brüdgam, Irene; Reißig, Hans‐Ulrich

doi:10.1002/ejoc.200800019

Cited by 23 publications

(17 citation statements)

References 61 publications

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“…Our serendipitous discovery constituted a new method to convert easily available aromatic compounds into functionalized dearomatized products with high synthetic potential. [8] For this reason we started a systematic investigation of this SmI 2 -induced reaction and successfully studied appropriately substituted ketones with aryl, [9] naphthyl, [10] pyrrolyl, [11] indolyl, [12] and quinolyl [13] groups as ac-ety are less favourable for the ketyl-aryl couplings. They apparently impede the second electron transfer that is involved in this multi-step process.…”

Section: Introductionmentioning

confidence: 99%

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Wefelscheid¹,

Berndt²,

Reißig³

2008

Eur J Org Chem

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This comprehensive study describes the influence of substituents at the aryl moiety on SmI 2 -mediated intramolecular ketyl-aryl coupling reactions. Differently substituted γ-aryl ketones were employed as precursors, which were directly prepared by Heck reactions of 4-penten-2-ol with the corresponding bromo-or iodobenzenes. After treatment with two equivalents of samarium diiodide γ-aryl ketones bearing electron-withdrawing substituents such as cyano, trifluoromethyl or carbonyl groups gave the expected hexahydronaphthalene derivatives as single diastereoisomers in most cases. The position of the substituents was also of crucial influence on the outcome; in several cases ipso-substitution leading to the formation of spiro compounds was observed. Electron-donating substituents at the aromatic moi-

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Section: Introductionmentioning

confidence: 99%

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Wefelscheid¹,

Berndt²,

Reißig³

2008

Eur J Org Chem

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“…Cyclization of SM12/alkylation with bromoacetonitrile:A ccording to the procedures above, indolyl ketone SM12 (345 mg, 0.95 mmol), SmI 2 (22.9 mL, 2.29 mmol) and HMPA( 1.71 g,9.55 mmol) were stirred until the color turned from purple to brownish. Then bromoacetonitrile (1.…”

Section: Methodsmentioning

confidence: 99%

“…3,102.7,114.4,117.5,129.0,148.0,148.5,148.7 (2d,6s,Ar), 168.7 (s, C-6), 194.6 (s, C-1) ppm. HRMS (ESI-TOF): calcd for C 19 (3 aR*,11aS*,11bR*,13 aS*) 3,3 2 ,9,10,11,11a,12,13,2,3lm]pyrrolo- [2,3-d]carbazole-1-carboxylate (PC3):T oasolution of pentacyclic compound PC2 (177 mg, 0.51 mmol) in CH 2 Cl 2 (50 mL) were added DMAP (20 mg, 0.16 mmol), Et 3 N( 101 mg, 1.00 mmol) and methyl chloroformate (100 mg, 1.24 mmol) at 0 8C. The activated catalyst was added to as olution of cyclization product TC16 (210 mg, 0.59 mmol) in MeOH (25 mL).…”

Section: Methodsmentioning

confidence: 99%

“…[2,3] The reaction proceeds under dearomatization [4] of the benzene ring and hence it is as ynthetically very valuable process that was subsequently investigated in detail under variation of the substituents at the benzene ring [5] and of the spaceru nit, [6] the type of carbonyl groups, or the reaction conditions. [9][10][11] Strong Lewis basess uch as hexamethylphosphoramide (HMPA) are required to increase the redox po-tential to al evel that allows the generation of reactive samarium ketyls. [9][10][11] Strong Lewis basess uch as hexamethylphosphoramide (HMPA) are required to increase the redox po-tential to al evel that allows the generation of reactive samarium ketyls.…”

Section: Introductionmentioning

confidence: 99%

“…[7] It was also extended to naphthalene derivatives that allowed the preparation of steroida nalogues [8] and to heteroarenes. [9][10][11] Strong Lewis basess uch as hexamethylphosphoramide (HMPA) are required to increase the redox po-tential to al evel that allows the generation of reactive samarium ketyls. [12] Tripyrrolidino phosphoric acid triamide (TPPA) can often serve as ag ood substitute for the toxic additive HMPA yieldingsatisfying conversionsinmany,but not in all examined cases.…”

Section: Introductionmentioning

confidence: 99%

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Stereoselective Cascade Cyclizations with Samarium Diiodide to Tetracyclic Indolines: Precursors of Fluorostrychnines and Brucine

Beemelmanns

Nitsch

Bentz

et al. 2019

Chemistry A European J

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As eries of g-indolylketones with fluorine, cyano or alkoxy substituents at the benzene moiety was prepared and subjected to samarium diiodide-promoted cyclization reactions. The desired dearomatizing ketyl cascade reaction formingt wo new rings proceeded in all cases with high diastereoselectivity,b ut with differing product distribution. In most cases, the desired annulated tetracyclic compounds were obtained in moderate to good yields, but as second product tetracyclic spirolactones were isolated in up to 29 % yield. The reaction rate was influencedb yt he substituents at the benzenem oiety of the substrate as expected, with electron-accepting groups acceleratingand electron-donating groups deceleratingt he cyclizationp rocess. In case of a difluoro-substituted g-indolylketone ap artial defluorination was observed.T he intermediate samarium enolateo ft he tetracyclic products could be trappedb ya dding reactive alkylating agents as electrophiles delivering products with quarternaryc arbons. In the case of ad imethoxy-substituted tetracyclic cyclization product as ubsequentr eductivea minations tereoselectively provided ap entacyclic compound that was subsequently N-protected and subjected to aregioselectivee limination.T he obtained functionalized pentacyclic product should be convertible into the alkaloid brucine by four well-established steps. Overall,t he presented report showst hat functionalized tetracyclic compounds with different substituents are rapidly availablew ith the samarium diiodidec ascade cyclization as crucial step. Hence, analogueso ft he landmarka lkaloid strychnine, fore xample, with specific fluorine substitutions, should be easily accessible.Scheme1.Samarium diiodide-promoted cyclizationso fN -acylatedindole derivatives A stereoselectively leadingt ot ricyclic compounds B and proposed transitions tate TS1.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi. Scheme5.Cascadec yclizations of fluoro-substituted indole derivatives SM3-SM7 leading to tetracyclic compounds TC3-TC7 and spirolactones SL3-SL7 and cyclizations of cyano-and alkoxy-substitutedi ndolederivatives SM8-SM12 to TC8-TC12 and SL8-SL12.

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Nine Times Fluoride can be Good for your Syntheses. Not just Cheaper: Nonafluorobutanesulfonates as Intermediates for Transition Metal‐Catalyzed Reactions

2009

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How much fluoride is good for a strong electron-withdrawing effect? In this review we summarize recent results on the use of perfluoroalkanesulfonates, in particular of the cost effective nonafluorobutanesulfonates (nonaflates), in transition metal-catalyzed reactions and a few other typical transformations. During the last decade many advantages over the commonly used triflates have been discovered. The generation of alkenyl and (het)aryl nonaflates and their applications in metal-catalyzed processes such as Heck, Suzuki, Sonogashira, Stille, and Negishi couplings or amination reactions are described. Although far from a systematic investigation, all the presented results clearly demonstrate the many advantages of nonaflates and of similar higher fluorinated sulfonates in laboratory and industrial scale organic synthesis.

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Nitrogen‐Containing Tricyclic and Tetracyclic Compounds by Stereoselective Samarium Diiodide Promoted Cyclizations of Quinolyl‐Substituted Ketones – A New Access to Azasteroids

Cited by 23 publications

References 61 publications

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Stereoselective Cascade Cyclizations with Samarium Diiodide to Tetracyclic Indolines: Precursors of Fluorostrychnines and Brucine

Nine Times Fluoride can be Good for your Syntheses. Not just Cheaper: Nonafluorobutanesulfonates as Intermediates for Transition Metal‐Catalyzed Reactions

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