Electrophilic Phosphonium Cations as Lewis Acid Catalysts in Diels–Alder Reactions and Nazarov Cyclizations

Vogler, Maria; Süße, Lars; LaFortune, James H. W.; Stephan, Douglas W.; Oestreich, Martin

doi:10.1021/acs.organomet.8b00496

Cited by 24 publications

(18 citation statements)

References 44 publications

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“…Its solubility increases in EG, resulting in a homogeneous reaction mixture, likely due to the formation of a eutectic system in the molar ratio employed (TPMPBr and EG 1/3). To the best of our knowledge, the reactions performed as indicated in entries 1, 3, and 5 in Table 1 [14].…”

Section: Resultsmentioning

confidence: 99%

“…The Nazarov reaction consists in the electrocyclization of divinyl ketones to cyclopentenones through a 4π conrotatory mechanism promoted by Bronsted (BA) or Lewis acids (LA). Many versions of such protocol have been recently developed, both in terms of substrates suitable for cyclization [6] and promoters, including transition metals catalysts [7][8][9][10][11], organocatalysts [12][13][14][15], and UV irradiation (photo-Nazarov reaction) [16].…”

Section: Introductionmentioning

confidence: 99%

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Optimization of Nazarov Cyclization of 2,4-Dimethyl-1,5-diphenylpenta-1,4-dien-3-one in Deep Eutectic Solvents by a Design of Experiments Approach

et al. 2020

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The unprecedented Nazarov cyclization of a model divinyl ketone using phosphonium-based Deep Eutectic Solvents as sustainable non-innocent reaction media is described. A two-level full factorial Design of Experiments was conducted for elucidating the effect of the components of the eutectic mixture and optimizing the reaction conditions in terms of temperature, time, and substrate concentration. In the presence of the Deep Eutectic Solvent (DES) triphenylmethylphosphonium bromide/ethylene glycol, it was possible to convert more than 80% of the 2,4-dimethyl-1,5-diphenylpenta-1,4-dien-3-one, with a specific conversion, into the cyclopentenone Nazarov derivative of 62% (16 h, 60 °C). For the reactions conducted in the DES triphenylmethylphosphonium bromide/acetic acid, quantitative conversions were obtained with percentages of the Nazarov product above 95% even at 25 °C. Surface Responding Analysis of the optimized data furnished a useful tool to determine the best operating conditions leading to quantitative conversion of the starting material, with complete suppression of undesired side-reactions, high yields and selectivity. After optimization, it was possible to convert more than 90% of the model substrate into the desired cyclopentenone with cis percentages up to 77%. Experimental validation of the implemented model confirmed the robustness and the suitability of the procedure, leading to possible further extension to this specific combination of experimental designs to other substrates or even to other synthetic processes of industrial interest.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Optimization of Nazarov Cyclization of 2,4-Dimethyl-1,5-diphenylpenta-1,4-dien-3-one in Deep Eutectic Solvents by a Design of Experiments Approach

et al. 2020

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“…Traditional examples of main-group Lewis acid catalysts involve group 13 and 14 elements as the central locus of reactivity,a stheyf eature al ow-lying orbital for substrate activation. [1] Over the last decade there has been increasing interest in studying pnictogens,o ften considered Lewis basic given the availability of an energetically accessible lone pair, in this unconventional role.T his work has been expanded to include compounds of phosphorus, [2][3][4][5][6][7][8][9][10][11] arsenic, [12] antimony, [13][14][15][16][17][18][19][20] and bismuth. [21][22][23] By contrast, the reactivity of nitrogen-containing compounds as Lewis acids has been investigated to am uch lesser extent, largely due to the dearth of such species.C hloramines,n itrenes,d iazocarboxylates,azides,and diazonium salts have been shown to possess N-centered electrophilic behavior.…”

Section: Nitrenium Salts In Lewis Acid Catalysismentioning

confidence: 99%

Nitrenium Salts in Lewis Acid Catalysis

Mehta

Goicoechea

2020

Angew Chem Int Ed

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Molecular compounds featuring nitrogen atoms are typically regarded as Lewis bases and are extensively employed as donor ligands in coordination chemistry or as nucleophiles in organic chemistry.B yc ontrast, electrophilic nitrogencontaining compounds are muchr arer.N itrenium cations are an ew family of nitrogen-based Lewis acids,t he reactivity of which remains largely unexplored. In this work, nitrenium ions are explored as catalysts in five organic transformations.These reactions are the first examples of Lewis acid catalysis employing nitrogen as the site of substrate activation. Moreover,these compounds are readily accessed from commercially available reagents and exhibit remarkable stability toward moisture,a llowing for benchtop transformations without the need to pretreat solvents.

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“…Over the last decade there has been increasing interest in studying pnictogens, often considered Lewis basic given the availability of an energetically accessible lone pair, in this unconventional role. This work has been expanded to include compounds of phosphorus, arsenic, antimony, and bismuth . By contrast, the reactivity of nitrogen‐containing compounds as Lewis acids has been investigated to a much lesser extent, largely due to the dearth of such species.…”

Section: Figurementioning

confidence: 99%

Nitrenium Salts in Lewis Acid Catalysis

Mehta

Goicoechea

2020

Angewandte Chemie

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Molecular compounds featuring nitrogen atoms are typically regarded as Lewis bases and are extensively employed as donor ligands in coordination chemistry or as nucleophiles in organic chemistry. By contrast, electrophilic nitrogen‐containing compounds are much rarer. Nitrenium cations are a new family of nitrogen‐based Lewis acids, the reactivity of which remains largely unexplored. In this work, nitrenium ions are explored as catalysts in five organic transformations. These reactions are the first examples of Lewis acid catalysis employing nitrogen as the site of substrate activation. Moreover, these compounds are readily accessed from commercially available reagents and exhibit remarkable stability toward moisture, allowing for benchtop transformations without the need to pretreat solvents.

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Electrophilic Phosphonium Cations as Lewis Acid Catalysts in Diels–Alder Reactions and Nazarov Cyclizations

Cited by 24 publications

References 44 publications

Optimization of Nazarov Cyclization of 2,4-Dimethyl-1,5-diphenylpenta-1,4-dien-3-one in Deep Eutectic Solvents by a Design of Experiments Approach

Optimization of Nazarov Cyclization of 2,4-Dimethyl-1,5-diphenylpenta-1,4-dien-3-one in Deep Eutectic Solvents by a Design of Experiments Approach

Nitrenium Salts in Lewis Acid Catalysis

Nitrenium Salts in Lewis Acid Catalysis

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