Generation and Reaction of Ammonium Ylides in Basic Two‐Phase Systems

Kowalkowska, Anna; Suchołbiak, Dorota; Jończyk, A.

doi:10.1002/chin.200527046

Cited by 7 publications

(9 citation statements)

References 1 publication

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“…For epoxidation, observed reactivity does not correlate with carbon nucleophilicity either. Sulfonium ylides react with aldehydes at temperatures as low as −78 °C,9 whilst room temperature is required using ammonium ylides 10. This is consistent with the energy profile3 for the reaction of the ylides 1 with benzaldehyde, and again, the higher reactivity of the sulfur‐based species is due to a lower barrier in the intramolecular substitution step (Figure 2).…”

Section: Computed3 Activation Energies (δE≠) and Reaction Energies (δsupporting

confidence: 79%

On the Importance of Leaving Group Ability in Reactions of Ammonium, Oxonium, Phosphonium, and Sulfonium Ylides

2005

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Dedicated to Professor Steven Ley on the occasion of his 60th birthday Ammonium, phosphonium, and sulfonium ylides are powerful and versatile reagents in organic chemistry, which undergo three important types of reaction: olefination, cyclization to a three-membered ring, and rearrangement.[1] The reactivity and selectivity of the ylides in these reactions depend on the nature of the central heteroatom. The nucleophilicity of the carbon centre of the ylides is one important aspect of their reactivity, which is affected by the degree to which the onium group stabilizes the adjacent negative charge. It has been shown that stabilization increases in the order O < N ! P < S.[2] However, this feature alone does not explain all the observed reactivity. We present comparative computational data which suggest that the differences are mainly due to the differing leaving group ability of the respective onium groups. The calculations [3] are carried out using the accurate B3LYP density functional, which is known to describe trends of the kind studied here accurately. [4,5] We also include a continuum solvent model in all calculations as the gas-phase potential energy surfaces are qualitatively inaccurate for some of these very polar species. [5] In the reaction with organoboranes, sulfonium ylides give homologation products at low temperature [6] while the more nucleophilic ammonium ylides react only at reflux of THF, [7] and phosphonium ylides require temperatures above 130 8C.[8]The energy profile [3] for the reaction of BMe 3 with ylides 1 involves barrierless addition to form ate complex 2, followed by rate-determining 1,2-migration (Figure 1). The first step is most exothermic for the ammonium and oxonium ylides while the barrier for migration is smallest with the oxonium ylide and largest with the phosphonium derivative. Nucleophilicity of the onium ylides is clearly irrelevant for this process, with the key factor being instead the leaving group ability of the onium group, which decreases in the order O > S > N > P.For epoxidation, observed reactivity does not correlate with carbon nucleophilicity either. Sulfonium ylides react with aldehydes at temperatures as low as À78 8C, [9] whilst room temperature is required using ammonium ylides.[10] This is consistent with the energy profile [3] for the reaction of the ylides 1 with benzaldehyde, and again, the higher reactivity of the sulfur-based species is due to a lower barrier in the intramolecular substitution step (Figure 2). In this reaction, the initial addition step is barrierless with the more nucleophilic ammonium ylide, and hence more favorable than with the sulfonium ylide, where a small barrier is observed. In the latter case, though, addition is the only demanding (and ratelimiting) step, whereas with nitrogen, betaine formation is followed by slower decomposition over a 15 kcal mol À1 barrier. This is consistent with the experimental observation that b-hydroxy ammonium salts are isolated upon work-up of the reaction of ammonium ylides at low temperature. [11...

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Section: Computed3 Activation Energies (δE≠) and Reaction Energies (δsupporting

confidence: 79%

On the Importance of Leaving Group Ability in Reactions of Ammonium, Oxonium, Phosphonium, and Sulfonium Ylides

2005

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“…Both cyclohexylaldehyde and butyraldehyde also afforded the desired triazole product in 95% and 98% isolated yield, respectively ( 17 and 18 ). More importantly, in all these cases, an epoxide product, which is well‐documented, was not observed ,…”

Section: Resultsmentioning

confidence: 57%

A Domino Reaction of Pyridinium Salts: Efficient Synthesis of 4,5‐Disubstituted 1,2,3‐(NH)‐Triazoles

2018

ChemistrySelect

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A one-pot mild and metal-free procedure for efficient synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles has been developed through the sequentially reaction of pyridinium salts with aldehydes and sodium azide. In the presence of L-proline, a key intermediate, an olefinic pyridinium-salt, is in situ generated via coupling of pyridinium salts with aldehydes and cyclizes with azide ion to form a triazole ring.

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“…Most of these methods suffer from one or several drawbacks such as low yield, long reaction time, tedious workup, use of toxic solvents, and expensive reagents. Moreover from the past few decades, multicomponent reactions have emerged as a powerful tool in the synthesis of complex and important biologically active molecules from easily available starting materials. Therefore to overcome the aforementioned problems and fulfill the criteria, we investigated and successfully implemented the sulfamic acid (SA) as the best and cheaper catalyst (which is a common sulfur‐containing amino acid with mild acidity and carries out many organic transformation under mild and user‐friendly conditions) for the preparation of poly‐substituted pyridines in aqueous medium and screened for antimicrobial activity (Tables and ).…”

Section: Introductionmentioning

confidence: 99%

Sulfamic Acid‐Catalyzed Multicomponent One‐Pot Synthesis of Poly‐Substituted Pyridines and Their Antimicrobial Activity

Banothu

Vijayalaxmi

Rajitha

2013

Journal of Heterocyclic Chem

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Generation and Reaction of Ammonium Ylides in Basic Two‐Phase Systems

Cited by 7 publications

References 1 publication

On the Importance of Leaving Group Ability in Reactions of Ammonium, Oxonium, Phosphonium, and Sulfonium Ylides

On the Importance of Leaving Group Ability in Reactions of Ammonium, Oxonium, Phosphonium, and Sulfonium Ylides

A Domino Reaction of Pyridinium Salts: Efficient Synthesis of 4,5‐Disubstituted 1,2,3‐(NH)‐Triazoles

Sulfamic Acid‐Catalyzed Multicomponent One‐Pot Synthesis of Poly‐Substituted Pyridines and Their Antimicrobial Activity

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