Reactivity of 1,3-dipoles in aqueous solution. 2. Stereospecific reactions of benzonitrile oxides with oxygen, carbon, and nitrogen nucleophiles

Dignam, Kieran J.; Hegarty, A. F.; Quain, Paul

doi:10.1021/jo00397a002

Cited by 70 publications

(17 citation statements)

References 18 publications

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“…www.prkm.co.uk Over years, researchers have reported examples of this reaction with stereospecific outcomes which seemed to imply concerted mechanisms [39][40][41]. After these numerous reports, the general belief was that the mechanism of 1,3-dipolar reaction was asynchronous concerted [26].…”

Section: A Brief Historymentioning

confidence: 99%

Beyond the Alternatives that Switch the Mechanism of the 1,3-Dipolar CyCloadditions from Concerted to Stepwise or Vice Versa: A Literature Review

Siadati

2016

Progress in Reaction Kinetics and Mechanism

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For several decades, the concerted or stepwise character of the mechanism of the 1,3-dipolar cycloaddition reaction has been one of the most debated issues in the field of organic chemistry. The significance of this problem is due to the fact that in a catalyst-free 1,3-dipolar cycloaddition, when the mechanism switches from concerted to stepwise, the stereospecificity is lost and thus unwanted stereoisomers may emerge. The first proposals about the mechanism of the 1,3-dipolar reaction were due to Huisgen (concerted model) and subsequently by Firestone (two-step diradical channel) in the 1960s. After a decade of debate, most researchers accepted the concerted model for the reaction, but during these years, researchers reported some examples of the stepwise mechanism for catalyst-free 1,3-dipolar cycloadditions. This review attempts to find a number of factors that could influence the reaction channels and switch the mechanism from concerted to stepwise, or vice versa.

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Section: A Brief Historymentioning

confidence: 99%

Beyond the Alternatives that Switch the Mechanism of the 1,3-Dipolar CyCloadditions from Concerted to Stepwise or Vice Versa: A Literature Review

Siadati

2016

Progress in Reaction Kinetics and Mechanism

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“…Alternatively, Plenkiewicz found that treatment of azidoxime 1Zb with an acid chloride in cyclohexane or benzene resulted in the formation of a tetrazole 9, 10. This reaction was later substantiated by Hegarty, who proposed a reversible acetylation–isomerization–cyclization pathway as indicated in Scheme 18, 19. In this pathway, the intermediate 6 has a less double bond character between the carbon and nitrogen due to resonance and can thereby rotate so that the Y substituent is ‘trans’ to the azide functionality ( 8 ).…”

Section: Resultsmentioning

confidence: 93%

Synthesis of N‐alkoxybenzimidoyl azides and their reactions in electrophilic media

Dolliver

Sommerfeld

Lanier

et al. 2009

J of Physical Organic Chem

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A new general route to N‐alkoxybenzimidoyl azides [ArC(N3)=NOR] from a reaction of N‐alkoxybenzimidoyl bromide [ArC(Br)=NOR] with sodium azide in DMSO is described. These reactions result in the Z‐geometric configuration. These compounds show a moderate degree of thermal stability as assessed by differential scanning calorimetry, and lack reactivity in traditional 1,3‐dipolar cycloaddition ‘click’ reactions. Upon exposure to electrophilic compounds (trifluoroacetic acid or acetyl chloride), these azide compounds can react by two pathways: a Schmidt‐type rearrangement to form an N‐alkoxyurea or an isomerization–cyclization reaction pathway to form an N‐alkoxytetrazole. The route of the reaction has no dependence on solvent polarity and appears to depend upon the electrophile (H+ vs. CH3CO+): reaction of the azide with trifluoroacetic acid results predominantly in the urea; reaction with acetyl chloride results solely in the tetrazole. Calculations indicate that the urea product is thermodynamically favored over the tetrazole product. They also indicate that both reaction conditions result in an equilibration between the starting azide and the tetrazole with the tetrazole being the major component in this equilibrium mixture. The fact that the azide also undergoes a Schmidt‐type rearrangement to form an N‐alkoxyurea when treated with trifluoroacetic acid appears to indicate that the barrier for aromatic ring migration is lower in the protonated azide produced on reaction with trifluoroacetic acid than in the acetylated azide produced on reaction with acetyl chloride. Copyright © 2009 John Wiley & Sons, Ltd.

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“…The oxime unit of 9 is configurationally homogeneous, however, an unambiguous E/Z assignment was not possible. It is known from the literature that additions of nucleophiles to nitrile oxides provide products with the hydroxyl group of the oxime at the side of the incoming nucleophile . The configuration of 9 (and that of intermediate 12 ) as depicted is hence fairly likely.…”

Section: Resultsmentioning

confidence: 99%

Reactions of Lithiated Methoxyallene with Oxime Derivatives - Formation of 1,2-Oxazines and Functionalized Isoxazole Derivatives

2016

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In a brief exploratory study we investigated the reactions of lithiated methoxyallene with different oxime derivatives. With E‐benzaldehyde oxime a 3,6‐dihydro‐2H‐1,2‐oxazine derivative was isolated in low yield, being the result of an overall [3+3] cyclization. The reaction of lithiated methoxyallene with phenylhydroximoyl chloride provided a moderate yield of an isoxazole derivative that incorporated two benzonitrile oxide‐derived moieties. In situ generated α‐nitrosostyrene and lithiated methoxyallene combine to the expected primary 1,4‐addition product which could be trapped by O‐methylation. On the other hand, the primary adduct cyclized after aqueous work‐up to give a vinyl‐substituted isoxazole derivative in good yield. Mechanisms for the formation of the products are presented. The discovered new routes to 1,2‐oxazine or isoxazole derivatives seem to be restricted to aryl‐substituted electrophiles.

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Reactivity of 1,3-dipoles in aqueous solution. 2. Stereospecific reactions of benzonitrile oxides with oxygen, carbon, and nitrogen nucleophiles

Cited by 70 publications

References 18 publications

Beyond the Alternatives that Switch the Mechanism of the 1,3-Dipolar CyCloadditions from Concerted to Stepwise or Vice Versa: A Literature Review

Beyond the Alternatives that Switch the Mechanism of the 1,3-Dipolar CyCloadditions from Concerted to Stepwise or Vice Versa: A Literature Review

Synthesis of N‐alkoxybenzimidoyl azides and their reactions in electrophilic media

Reactions of Lithiated Methoxyallene with Oxime Derivatives - Formation of 1,2-Oxazines and Functionalized Isoxazole Derivatives

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