New syntheses of the amaryllidacaea alkaloids vasconine assoanine, oxoassoanine, pratosine and ismine by radical cyclisation

Rosa, Ana M.; Lobo, Ana M.; Branco, Paula S.; Prabhakar, Sundaresan; Costa, M. Sá da

doi:10.1016/s0040-4020(96)00985-4

Cited by 44 publications

(17 citation statements)

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“…Vasconine 123 , along with assoanine, oxoassoanine, pratosine and ismine, constitute another group of alkaloids, isolated from Narcissus plants of the Amaryllidaceae family, that contain phenanthridine rings [125,126]. The acyl oxime 121 was targeted as a key compound and prepared in six steps from commercial 2-(3-bromophenyl)ethanol [52].…”

Section: Iminyl Radical Mediated Preparations Of Natural Products mentioning

confidence: 99%

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Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

Walton

2016

Molecules

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Abstract:The totality of chemical space is so immense that only a small fraction can ever be explored. Computational searching has indicated that bioactivity is associated with a comparatively small number of ring-containing structures. Pyrrole, indole, pyridine, quinoline, quinazoline and related 6-membered ring-containing aza-arenes figure prominently. This review focuses on the search for fast, efficient and environmentally friendly preparative methods for these rings with specific emphasis on iminyl radical-mediated procedures. Oxime derivatives, particularly oxime esters and oxime ethers, are attractive precursors for these radicals. Their use is described in conventional thermolytic, microwave-assisted and UV-vis based preparative procedures. Photoredox-catalyzed protocols involving designer oxime ethers are also covered. Choice can be made amongst these synthetic strategies for a wide variety of 5-and 6-membered ring heterocycles including phenanthridine and related aza-arenes. Applications to selected natural products and bioactive molecules, including trispheridine, vasconine, luotonin A and rutaecarpine, are included.

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Section: Iminyl Radical Mediated Preparations Of Natural Products mentioning

confidence: 99%

“…UV irradiation of this through Pyrex in MeCN solution afforded phenanthridinylethanol derivative 122 in 53% yield (Scheme 20). Compound 122 can be converted to vasconine 123 by treatment with PBr 3 and can also act as precursor for assoanine, oxoassoanine, and pratosine [125].…”

Section: Iminyl Radical Mediated Preparations Of Natural Products mentioning

confidence: 99%

Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

Walton

2016

Molecules

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“…As shown in Scheme 21, the use of a combination of reagents with five-and six-membered rings and cyclization of the intermediate iminyl radicals onto phenyl, thiophenyl or pyridinyl rings led to a variety of fused rings with different heteroatoms on the structure in good to excellent yields (48 to 90%) (Alonso et al, 2010 The versatility of this methodology has been exploited in the preparation of some interesting natural products. On using the appropriate structure (Scheme 22), direct irradiation of Oacyloximes allowed the preparation of several phenanthridine derivatives (Alonso et al, 2010), such as the alkaloid trisphaeridine (R 1 ,R 2 = OCH 2 O; R 3 = H ) o r t h e v a s c o n i ne precursor (R 1 = R 2 = OCH 3 ; R 3 = CH 2 CH 2 OH), which can also be used to obtain assoanine, oxoassoanine and pratosine (Rosa et al, 1997). Trisphaeridine was also prepared in 59% yield by irradiation of the corresponding dioxime oxalate in the presence of 4-methoxyacetophenone as a photosensitizer (Portela-Cubillo et al, 2008).…”

Section: Preparation Of Polycyclic Heteroaromatic Compounds and Naturmentioning

confidence: 99%

Light-Induced Iminyl Radicals: Generation and Synthetic Applications

Barranco¹

2012

Molecular Photochemistry - Various Aspects

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“…5 Construction of the C aryl -C aryl bond by radical cyclization is very difficult and the yield of the reaction is very low. 6 Therefore, as part of our on-going research work for the construction of linear, as well as angularly fused, polynuclear heterocycles by biaryl coupling, we planned to apply palladium(0)-catalyzed reactions. The palladium(0)-catalyzed arylation of alkenes or arenes provides a versatile route to the construction of complex cyclic systems.…”

Section: Figurementioning

confidence: 99%

Highly Effective Regioselective Method for the Synthesis of Substituted Coumarin- and Quinolone-Annulated Heterocycles Using a Palladium(0)-Catalyzed Reaction

Majumdar¹,

Pal²,

Taher³

et al. 2007

Synthesis

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The preparation of a variety of tetracyclic ring systems by palladium(0)-catalyzed cyclization of 2-bromobenzyloxy-substituted coumarins and quinolones is described. The process has been found to be a viable method for regioselective synthesis of the corresponding products in very good to excellent yield.Several linear and angular pyranocoumarins and quinolones, like xanthyletin (I), seseline (II), flindersine (III) ( Figure 1) and various flindersine derivatives, are widely distributed in nature 1a-j and also possess a broad spectrum of biological activities. 1h-k Xanthyletin exhibits 1i antifungal insecticidal, anticancer, and anti-HIV activities, while seseline is used as a photoactive drug for skin disorders. 1j A great deal of work has been done towards the synthesis of these compounds. 1i-k,2 Figure 1So far we have utilized the Claisen rearrangement, radical cyclization, and ene-yne ring-closing metathesis for the synthesis of polynuclear coumarin and quinolone annulated heterocycles. 3 The Claisen rearrangement has been a very important reaction since 1912 and we have been able to construct C-C bonds with high a degree of regioselectivity. 4 On the other hand radical cyclizations have emerged as a valuable tool for the construction of polynuclear heterocyclic compounds. 5 Construction of the C aryl -C aryl bond by radical cyclization is very difficult and the yield of the reaction is very low. 6 Therefore, as part of our on-going research work for the construction of linear, as well as angularly fused, polynuclear heterocycles by biaryl coupling, we planned to apply palladium(0)-catalyzed reactions. The palladium(0)-catalyzed arylation of alkenes or arenes provides a versatile route to the construction of complex cyclic systems. 7 Herein we report palladium(0)-catalyzed intramolecular reactions on coumarin and quinolone derivatives.For the synthesis of tetracyclic coumarin-and quinoloneannulated heterocycles, we selected compound 3a-l as starting materials. They were, in turn, prepared by the alkylation of different hydroxycoumarins and -quinolones with various substituted 2-bromobenzyl bromides 2a,b. Compound 3a was prepared by using a classical alkylation procedure according to which 7-hydroxycoumarin (1a) was dissolved in anhydrous acetone and to this 2-bromobenzyl bromide (2a) and potassium carbonate were added and the reaction mixture was refluxed for four hours to afford a white solid in 82% yield. The structure of the product was determined to be 3a by elemental analysis and spectroscopic data. Encouraged by the initial success, we prepared other substrates 3b-d from 7-and 6-hydroxycoumarin under the same reaction conditions (Scheme 1). Other aryl ethers 3e-l were synthesized according to published procedures. 8 Scheme 1 Reagents and conditions: anhyd acetone, K 2 CO 3 , reflux, 4-5 h.Compound 3a is susceptible to palladium(0)-catalyzed intramolecular annulation reactions. Compound 3a (0.60 mmol) was dissolved in anhydrous N,N-dimethylformamide (25 mL) and stirred with palladium(II) acetate (10 mol%...

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New syntheses of the amaryllidacaea alkaloids vasconine assoanine, oxoassoanine, pratosine and ismine by radical cyclisation

Cited by 44 publications

References 20 publications

Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

Light-Induced Iminyl Radicals: Generation and Synthetic Applications

Highly Effective Regioselective Method for the Synthesis of Substituted Coumarin- and Quinolone-Annulated Heterocycles Using a Palladium(0)-Catalyzed Reaction

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New syntheses of the amaryllidacaea alkaloids vasconine assoanine, oxoassoanine, pratosine and ismine by radical cyclisation

Cited by 44 publications

References 20 publications

Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

Synthetic Strategies for 5- and 6-Membered Ring Azaheterocycles Facilitated by Iminyl Radicals

Light-Induced Iminyl Radicals: Generation and Synthetic Applications

Highly Effective Regioselective Method for the Synthesis of Substituted Coumarin­- and Quinolone-Annulated Heterocycles Using a Palladium(0)-Catalyzed­ Reaction

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Product

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Highly Effective Regioselective Method for the Synthesis of Substituted Coumarin- and Quinolone-Annulated Heterocycles Using a Palladium(0)-Catalyzed Reaction