5.20 Claisen Rearrangements

Martín-Castro, A. M.; Tortosa, Mariola

doi:10.1016/b978-0-08-097742-3.00521-8

Cited by 10 publications

(12 citation statements)

References 380 publications

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“…The aromatic Claisen rearrangement is one of the most powerful synthetic tools for functionalization of arenes. [1][2][3][4] This classic [3,3]-rearrangement reaction generally requires the pre-synthesis of relatively stable rearrangement precursors (e.g. allyl phenyl ethers).…”

Section: Introductionmentioning

confidence: 99%

“…1A). [5][6] The subsequent [3,3]-rearrangement occurs spontaneously leading to synthetically appealing ortho-functionalized aryl iodides. In the past three decades, an array of nucleophiles such as allyl/propargyl silanes, [7][8][9][10][11][12][13][14] carbonyl compounds, 15,16 phenols, 17 α-stannyl nitriles, [18][19][20][21] and enol silyl ethers 22 have been found to be suitable for the rearrangement process.…”

Section: Introductionmentioning

confidence: 99%

“…23 Owing to the more precisely control of the process, the indirect strategy not only signi cantly broadened the scope of nucleophiles but also enabled the reaction to proceed in a 3D-controlled manner. Inspired by this progress, we herein report our endeavour to advance the indirect protocol to achieve [3,3]-rearrangement of aryl iodanes with α,β-unsaturated carbonyls. Unlike the assembly/deprotonation approach to generate the rearrangement precursor, the present reaction passes through a precursor formed via a strategy which can be characted as "assembly/addition".…”

Section: Introductionmentioning

confidence: 99%

“…The LB addition then affords an iodine(III)-enolate species that could be an ideal rearrangement precursor. Subsequent [3,3]-rearrangement and β-elimination take place, nally producing valuable α-aryl α,β-unsaturated carbonyls that have signi cant utility in chemical synthesis [29][30][31][32][33] but may be di cult to make with E/Z selectivity through other known methods [34][35][36] . It should be noted that, while our study was underway, Wengryniuk reported an elegant iodonio-Claisen rearrangement of β-pyridinium silyl enol ethers that allows for α-arylation of α,β-unsaturated ketones.…”

Section: Introductionmentioning

confidence: 99%

“…37 However, the generation of βpyridinium silyl enol ethers has long been suffering from limited substrate scope [38][39][40] that restricts the scope of Wengryniuk's protocol to structurally de ned cyclic enones. As such, new reaction patterns are required for implementing iodonium- [3,3]-rearrangement of simple α,β-unsaturated carbonyls and overcoming the potential E/Z selectivity issue (Fig. 1D).…”

Section: Introductionmentioning

confidence: 99%

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Morita-Baylis-Hillman Reaction Inspired [3,3]-Rearrangement of Aryl Iodanes with α,β-Unsaturated Oxazolines

Zhang¹,

Bao²,

Liang³

et al. 2020

Preprint

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The [3,3]-rearrangement of aryl iodanes with α,β-unsaturated oxazolines has been developed by merging Morita-Baylis-Hillman (MBH) process into the rearrangement reaction. The method allows for the exclusively E-selective synthesis of a wide variety of valuable α-aryl α,β-unsaturated oxazolines which can be difficult to synthesize with other known methods. Experimental and computational mechanistic studies unraveled that the reaction proceeds via the assembly of both coupling partners followed by MBH-type addition to form rearrangement precursor, [3,3]-rearrangement, and stepwise E1cb-elimination. The E-selectivity of the reaction is favored both kinetically and thermodynamically.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Morita-Baylis-Hillman Reaction Inspired [3,3]-Rearrangement of Aryl Iodanes with α,β-Unsaturated Oxazolines

Zhang¹,

Bao²,

Liang³

et al. 2020

Preprint

View full text Add to dashboard Cite

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Radical [1,3] Rearrangements of Breslow Intermediates

Alwarsh

Qian

et al. 2015

Angewandte Chemie

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Breslow intermediates that bear radical stabilizing N-substituents including benzyl, cinnamyl, and diarylmethyl undergo facile homolytic C-N bond scission under mild conditions to give products of formal [1,3]-rearrangement rather than benzoin condensation. EPR experiments and computational analysis support a radical mechanism. Implications for thiamine based enzymes are discussed. Keywords N-heterocyclic carbene; Breslow intermediate; radical; rearrangement; thiamineThiamine diphosphate (TDP) is an essential cofactor for all living things. It is involved in several critical metabolic processes, including the tricarboxylic acid cycle, the pentose phosphate pathway, and amino acid catabolism. 1,2 In 1958, Ronald Breslow postulated that key intermediates in thiamine catalyzed enzymatic pathways included an N-heterocyclic carbene (1) and an enaminol, e.g. 2 (Scheme 1). 3 In pyruvate decarboxylation, for example, addition of the TDP carbene to pyruvate is followed by extrusion of CO 2 to provide unstable enaminol 2. This and related heterocyclic enaminols have collectively been called "Breslow intermediates." 4 Only recently have such compounds been rigorously characterized, 5,6 and new chemistry continues to be revealed. 7 We recently reported that Breslow intermediates such as 2a derived from N-allyl benzothiazolium bromide and aromatic aldehydes could be captured in a unique Claisen rearrangement to provide 2-butenyl benzothiazoles (Scheme 2, R=H). 8,9 In the course of examining the scope of the reaction, we were surprised to find that N-cinnamyl substituted salt 3b provided principally [1,3]-rearrangement product 4b upon reaction with benzaldehyde, accompanied by only ca. 5% of the nominal [3,3]-product. The [1,3]-rearrangement product clearly implied a stepwise process in competition with the concerted rearrangement.Correspondence to: Matthias C. McIntosh, mcintosh@uark.edu. Supporting information for this article is given via a link at the end of the document. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptReaction of N-benzyl and N-diphenylmethyl benzothiazolium salts under the same conditions also yielded [1,3]-rearrangement products, albeit in diminished yield in the case of benzyl salt 3c (Scheme 3). The structures were confirmed by X-ray crystallography.Many NHC catalyzed reactions of aldehydes are presumed to proceed via a Breslow intermediate, 10 so these observations are relevant to NHC catalysis and catalyst design. Since benzothiazolium salts are only occasionally employed as NHC catalysts, 11 we exposed thiazolium and triazolium salts to the reaction conditions (Scheme 4). Reaction of thiazolium salt 3e with benzaldehyde gave high yield of [1,3]-rearrangement product 4e, as well as a few percent of ketone 5e. Treatment of symmetrically substituted 1,2,4-triazole 3f provided rearrangement product 4f in low yield as the only isolable product, although interestingly as a single regioisomer resulting from migration of the N-4 substituent. No significant ...

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