Studies on intramolecular cycloadditions involving 3-oxidopyridinium

Bromidge, Steven M.; Archer, D. A.; Sammes, Peter G.

doi:10.1039/p19900000353

Cited by 17 publications

(6 citation statements)

References 19 publications

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“…The yield of the cycloadduct 476 was low but was improved later (to 64%) by heating in an autoclave at 160 °C. 182 A related cycloaddition was achieved using the pyridinium ylides 477a-c, prepared in the same way as the ylide 475 (Scheme 122). 183 Thermolysis of the ylides 477a-c in refluxing xylene gave the cycloadducts 478a-c in poor to reasonable yields (Table 11).…”

Section: Ylides From Pyridines and Pyrazinesmentioning

confidence: 99%

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Intramolecular Dipolar Cycloaddition Reactions of Azomethine Ylides

2005

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Section: Ylides From Pyridines and Pyrazinesmentioning

confidence: 99%

“…Subsequent thermolysis of 475 initiated cycloaddition of the ylide (aided by the 3-oxo substituent) with the pendant alkene and took place across the 2,6-positions of the pyridine ring. The yield of the cycloadduct 476 was low but was improved later (to 64%) by heating in an autoclave at 160 °C 121 …”

Section: 3 Ylides From Pyridines and Pyrazinesmentioning

confidence: 99%

Intramolecular Dipolar Cycloaddition Reactions of Azomethine Ylides

2005

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“…This class of betaines constitutes moderately reactive aza-1,3-dipoles that undergo dipolar cycloadditions at the 2-and 6-positions with alkenes and alkynes to produce tropanone-like adducts of varying complexity, including a handful of examples that proceed in an intramolecular mode. [70][71][72][73][74][75][76] In applying this approach to the synthesis of the hetisine alkaloids, the initial aim was to prepare the 3-oxidopyridinium betaine 50 (Scheme 8), incorporating a pendant ene-nitrile as an electronically activated, less sterically demanding dipolarophile. Although N-alkylation of substituted pyridines is the most direct and common method for the preparation of 3-oxipyridinium betaines, [63] concerns with nucleophilic substitution at a neopentyl carbon to form the N-C19 bond in 50 directed our efforts to pursuing an alternate approach involving the aza-Achmatowicz reaction.…”

Section: Intramolecular 13-dipolar Cycloadditions With 3-oxidopyridimentioning

confidence: 99%

Asymmetric Synthetic Access to the Hetisine Alkaloids: Total Synthesis of (+)‐Nominine

Peese

Gin

2008

Chemistry A European J

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A dual cycloaddition strategy for the synthesis of the hetisine alkaloids has been developed, illustrated by a concise asymmetric total synthesis of (+)-nominine (7). The approach relies on an early-stage intramolecular 1,3-dipolar cycloaddition of a 4-oxido-isoquinolinium betaine dipole with an enenitrile dipolarophile. Subsequent late-stage pyrrolidine-induced dienamine isomerization/DielsAlder cascade allows for rapid construction of the carbon-nitrogen polycyclic skeleton within this class of C 20 -diterpenoid alkaloids.

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“…Pyridinium oxide 15 featured ad ipolarophilet ethered to the pyridinium ring, rather than the nitrogen atom, and it gave the topologicallyd istinct bicycle 16. [12] It is notable that these intramolecular examples do not require ap olarizedd ipolarophile, and simple terminal alkenes participate in the reaction.…”

mentioning

confidence: 99%

“…[15] The reversibility in Gin's cycloaddition was attributed to the polarized vinyl sulfone dipolarophile. [12] However, we began to suspect our reactions with relatively non-polarized dipolarophiles were under thermodynamic control as well. We noticed that the product ratios were often somewhat variable, and more forcing conditions (higher tem- To investigate the reversibility of the reaction,s ubstrate 43 was selected because in earlyi nvestigations we observed stereoselectivities that seemedt ov ary with temperature.…”

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confidence: 99%

Intramolecular Pyridinium Oxide Cycloadditions: Systematic Study of Substitution, Diastereoselectivity, and Regioselectivity

Dey

Beaudry

2021

Chemistry A European J

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Intramolecular pyridinium oxide cycloadditions form complex polycyclic nitrogenous architectures. The diastereoselectivity and regioselectivity of pyridinium oxide cycloadditions was systematicallyi nvestigated for the first time using complex substrates. Predictably high levels of diastereoselectivity and regioselectivity are observed, which can be attributed to minimization of steric (syn-pentane) and torsional strain in the products. The reaction is reversible under the reaction conditions, and it is stereospecific with respectt ot he dipolarophile geometry. Polycyclic nitrogenous architectures are widespreadi nb iologically active natural products. For example, the tropane alkaloids, exemplified by cocaine, are characterized by a8-aza-bicyclo[3.2.1]octane structure, 1. [1] Amaryllidaceae alkaloidss uch as siculine display at opologically distinct 1-azabicyclo[3.2.1]octane core (2). [2] Homopumiliotoxin 223G is aq uinolizidine alkaloid (3)i solated from poison dart frogs. [3] Finally,t he intriguing structure of the galbulimima alkaloid, himgaline, displays all of these component aza-bicyclic fragments in a2-azatricyclo[4.4.1.0 2,7 ]undecane architecture (4)(Figure 1). [4, 5] Such bridged polycyclic alkaloids represent enduring challenges for synthetic chemists. An otable difficulty associated with the synthesis of the natural products shown are the ste-reogenic carbonsb earing nitrogen. [6] In particular,a ll three carbons bearingt he nitrogen atom in the himgaline structure are stereogenic,m aking this target notably complex. Many synthetic strategies have appeared to access nitrogenous bicycles, and particularly successful approaches create multiple rings in as ingle transformation with control of stereochemical outcomes. [7] Cycloadditionr eactions are particularly well suited for the challenge of preparing multiple rings with controlo fs tereochemistry,a nd we wonderedi fs uch polycyclic nitrogenous frameworks could be prepared using as uitablec ycloaddition. We decided to focus on the tricyclic motif found in himgaline, complete with the equatorial methyl substituent (5,S cheme 1). Any method capable of preparing this tricyclica rchitecture could,a tl east in principle, be used to construct any of the component bicyclic structures (1-3).

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Studies on intramolecular cycloadditions involving 3-oxidopyridinium

Cited by 17 publications

References 19 publications

Intramolecular Dipolar Cycloaddition Reactions of Azomethine Ylides

Intramolecular Dipolar Cycloaddition Reactions of Azomethine Ylides

Asymmetric Synthetic Access to the Hetisine Alkaloids: Total Synthesis of (+)‐Nominine

Intramolecular Pyridinium Oxide Cycloadditions: Systematic Study of Substitution, Diastereoselectivity, and Regioselectivity

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