Reactivity of the thiazolium C2 ylide in aprotic solvents: novel experimental evidence for addition rather than insertion reactivity

Chen, Yao-Tsung; Jordan, Frank

doi:10.1021/jo00017a010

Cited by 65 publications

(58 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Chen and Jordan used C(2)-labelled thiazolium salts to demonstrate that nucleophilic attack of a thiazol-2-ylidene 6 occurs at the C(2) position of a second thiazolium ion. [10] In this regard, the first step in these dimerization reactions is presumed to be the deprotonation of the first imidazolium component 4 followed by reaction of the resulting carbene 9 at the second imidazolium centre (Scheme 2). The tethered bis-propyl linked bis-imidazolium 4 can generate the tetraazafulvalene 1, whereas the analogous butyl linked system only generates the bis-carbene.…”

Section: Introductionmentioning

confidence: 99%

Proton transfer reactions of a bridged bis‐propyl bis‐imidazolium salt

Massey

Quinn

Zhou

et al. 2016

J of Physical Organic Chem

View full text Add to dashboard Cite

Tetraazafulvalene 1 has found broad application in reduction and other related transformations and is conveniently generated from bis‐propyl bis‐imidazolium salt 4 with a strong base in a non‐protic solvent. The proposed mechanism for the formation of 1 involves initial deprotonation at C(2) to give a mono‐carbene 9 followed by intramolecular reaction at the second azolium centre. Herein, we report the second‐order rate constants for deuteroxide‐catalysed exchange in aqueous solution of the C(2)‐hydrogens of bis‐propyl bis‐imidazolium di‐iodide salt 4 and related monomeric dipropyl imidazolium iodide 10 of kDO = 1.37 × 104 and 1.79 × 102 M−1 s−1, respectively, and used these data to calculate pKa values of 21.2 and 23.1. The greater C(2)‐H acidity of the doubly bridged bis‐propyl bis‐imidazolium salt 4 relative to 10 may be attributed to the inductive or electrostatic destabilization of the conjugate acid dicationic azolium ion 4 relative to the monocationic carbene 9, which is enhanced by bis‐tethering. Formation of tetraazafulvalene 1 was not observed under the aqueous conditions employed highlighting that carbene reprotonation significantly outcompetes dimerization under these conditions. Copyright © 2016 John Wiley & Sons, Ltd.

show abstract

Section: Introductionmentioning

confidence: 99%

Proton transfer reactions of a bridged bis‐propyl bis‐imidazolium salt

Massey

Quinn

Zhou

et al. 2016

J of Physical Organic Chem

View full text Add to dashboard Cite

show abstract

“…While we did not employ alkyl bromides in these reactions, we do believe based on our preliminary results that the use of alkyl iodides was dictated by their much higher reactivity than their bromide or chloride analogs. Although many literature methods are available for the synthesis of N-alkyl benzothiazolium iodides they require long reaction times, 18,19 use of excess alkyl halide 20 and the use of a solvent in order to obtain close to 100% yields. 21 Our initial attempts to synthesize N-methylbenzothiazolium iodide using solvent-free conditions in the reaction of benzothiazole with iodomethane at different temperatures were successful, but the yield of the product was not comparable with the previously reported method.…”

Section: Resultsmentioning

confidence: 99%

Solvent-free synthesis of benzothiazole-based quaternary ammonium salts: precursors to ionic liquids

Nadeem¹,

Munawar²,

Ahmad³

et al. 2010

Arkivoc

View full text Add to dashboard Cite

This paper is dedicated to Professor Richard A. Bartsch on the occasion of his 70thbirthday and retirement Abstract A series of 13 benzothiazolium iodide salts have been prepared in solvent-free conditions by optimizing the reaction. An additional 26 benzothiazolium salts with bistrifluoromethanesulfonimide and trifluoromethylsulfonate were prepared via simple metathesis reactions from the iodide precursors. Out of a total of 39 prepared salts, 26 were identified as ionic liquids, with melting points as low as 42 o C observed for dodecylbenzothiazolium bistrifluoromethanesulfonimide. All prepared compounds have been characterized using FTIR, 1 H, 13 C NMR, and HRMS analyses. The thermal stabilities as well as melting points of these salts were also analyzed.

show abstract

“…Therefore, in water, our negatively charge-tagged catalyst is probably not different enough in basicity as compared to more commonly used neutral counterparts to significantly affect catalytic ability. Last, we consider the "dimer mechanism," which over the years has been invoked as a possible alternate to the Breslow mechanism (Scheme 3) [29][30][31][32][33][34][35][36][37][38][39][40][41]. Several ions have the same m/z ratios (220, 326) as other ions in the Breslow mechanism.…”

Section: Mechanistic Commentsmentioning

confidence: 99%

“…Mechanisms involving a thiazolylidene dimer (first proposed by Lemal) have also been proposed; data both in support of and against such mechanisms exist [29][30][31][32][33][34][35][36][37][38][39][40][41] Because of the ever-growing prevalence and synthetic utility of reactions catalyzed by ylidenes, we sought to explore the potential of using ESI-MS to track such reactions, focusing on the classic benzoin condensation. Because the intermediates are not charged, the reaction is potentially difficult to track using mass spectrometry.…”

mentioning

confidence: 99%