Synthesis of methyl ketones from terminal olefins using PdCl2/CrO3 system mimicking the Wacker process

Fernandes, Rodney A.; Bethi, Venkati

doi:10.1016/j.tet.2014.05.022

Cited by 28 publications

(8 citation statements)

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“…[5][6] Efforts to replace the copper salts with other electron-transfer mediators to facilitate the re-oxidation of Pd(0) have met with some success, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] as have efforts to employ alternative oxidants. [25][26][27][28] Direct aerobic oxidations of alkenes in the absence of mediators are also known, [29][30][31][32][33][34][35][36][37][38] but for the oxidation of styrenes, [33][34] these systems typically require high loadings of Pd catalyst (5-10 mol %) and lengthy reaction times. The Muldoon group recently reported an efficient catalytic oxidation of styrenes with hydrogen peroxide (H2O2) in the presence of cationic Pd complexes ligated with 2-(pyridin-2-yl)benzoxazole (PBO), [(PBO)Pd(NCMe)2][OTf]2, (A, Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

“…Despite recent advances, − many challenges remain. The Wacker process for aerobic oxidation of ethylene to acetaldehyde with palladium chloride/copper chloride is a textbook example of industrial oxidation of an alkene; however, this catalyst system is typically less effective for alkenes other than ethylene. , Efforts to replace the copper salts with other electron-transfer mediators to facilitate the reoxidation of Pd(0) have been met with some success, − as have efforts to employ alternative oxidants. − …”

Section: Introductionmentioning

confidence: 99%

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Mechanism of Catalytic Oxidation of Styrenes with Hydrogen Peroxide in the Presence of Cationic Palladium(II) Complexes

et al. 2017

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Kinetic studies, isotope labeling, and in situ high-resolution mass spectrometry are used to elucidate the mechanism for the catalytic oxidation of styrenes using aqueous hydrogen peroxide (HO) and the cationic palladium(II) compound, [(PBO)Pd(NCMe)][OTf] (PBO = 2-(pyridin-2-yl)benzoxazole). Previous studies have shown that this reaction yields acetophenones with high selectivity. We find that HO binds to Pd(II) followed by styrene binding to generate a Pd-alkylperoxide that liberates acetophenone by at least two competitive processes, one of which involves a palladium enolate intermediate that has not been previously observed in olefin oxidation reactions. We suggest that acetophenone is formed from the palladium enolate intermediate by protonation from HO. We replaced hydrogen peroxide with t-butyl hydroperoxide and found that, although the palladium enolate intermediate was observed, it was not on the major product-generating pathway, indicating that the form of the oxidant plays a key role in the reaction mechanism.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanism of Catalytic Oxidation of Styrenes with Hydrogen Peroxide in the Presence of Cationic Palladium(II) Complexes

et al. 2017

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“…In an attempt to replace the copper co-catalyst, alternative electron transfer-mediator systems, such as polyoxometalates, 4 metal macrocycle/quinone combinations, 5 or benzoquinone/NaNO 2 / HClO 4 , 6 have been reported. Some researchers have also utilised oxidants such as benzoquinone 7 iron(III) sulphate, 8 chromium trioxide, 9 and potassium bromate. 10 Using O 2 as the sole oxidant is attractive, and a number of methods have been developed which utilise O 2 for the direct re-oxidation of Pd(0).…”

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confidence: 99%

Cationic palladium(ii) complexes as catalysts for the oxidation of terminal olefins to methyl ketones using hydrogen peroxide

Cao

Bailie

et al. 2015

Green Chem.

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COMMUNICATIONThis journal is Ligated Pd(II) complexes have been studied for the catalytic oxidation of terminal olefins to their corresponding methyl ketones. The method uses aqueous hydrogen peroxide as the terminal oxidant; a sustainable and readily accessible oxidant. The choice of ligand, counterion and solvent all have a significant effect on catalytic performance and we were able to develop systems which perform well for these challenging oxidations.

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“…of aqueous NaOH which gave rise to cyclic nitrone 26 in 50 % yield. However, other ketones like acetoin ( 3 ), TBS‐protected acetoin, and 1‐(benzyloxy)‐2‐propanone did not give the desired products. Based on the literature precedence we hoped that aldehydes would react better with 2‐hydroxyimino esters as compared to ketones.…”

Section: Resultsmentioning

confidence: 99%

Total Synthesis of the Natural Herbicide MBH‐001 and Analogues

et al. 2020

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The first total synthesis of the natural herbicide MBH-001 (1) is reported. Structurally it is a 2-methyloxazol-5(2H)-one with a (1-hydroxyethyl) substituent at the 2-position. By relying on cyclic nitrones, a flexible route to MBH-001 and relevant analogues was developed. Key steps include the reaction of a 2-hydroxyimino ester with an aldehyde to form a 5-oxo-2,5dihydrooxazole 3-oxide. In an aldol-type reaction, the anion of these cyclic nitrones reacted with an aldehyde at the 2-position.[a] Scheme 1. Retrosynthetic considerations for MBH-001 (1) and the issue of regioselectivity in reactions of oxazolones with electrophiles. Results and DiscussionInitial studies were performed on oxazolone 4b, obtained by the Steglich method from acylated amino acid [6] 10 using water soluble carbodiimide [7] 11 (Scheme 2). Reaction of aromatic aldehydes 12a-c with oxazolone 4b (isomer of 4a) in the presence of triethylamine or diisopropylethylamine (Hünig′s base) provided the desired addition products with the carbinol connected to C2 (Scheme 2). However, preliminary tests showed that these aryl analogues 13a-13c of MBH-001 have no significant herbicidal activity.Unfortunately, the reaction of oxazolone 4b with acetaldehyde under identical conditions took a different course (Scheme 3). Thus, it seems hydroxyalkylation takes places at C4 to form intermediate A. This intermediate could not be isolated since it reacted with another acetaldehyde molecule to intermediate B followed by opening of the oxazolone ring and formation of 1,3-dioxanone 14, whose structure was confirmed by a single-crystal X-ray diffraction. We cannot rule out that other stereoisomers are formed in this transformation. The aldol-like reaction between 4b and acetaldehyde might be diastereo-Eur.

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Synthesis of methyl ketones from terminal olefins using PdCl2/CrO3 system mimicking the Wacker process

Cited by 28 publications

References 57 publications

Mechanism of Catalytic Oxidation of Styrenes with Hydrogen Peroxide in the Presence of Cationic Palladium(II) Complexes

Mechanism of Catalytic Oxidation of Styrenes with Hydrogen Peroxide in the Presence of Cationic Palladium(II) Complexes

Cationic palladium(ii) complexes as catalysts for the oxidation of terminal olefins to methyl ketones using hydrogen peroxide

Total Synthesis of the Natural Herbicide MBH‐001 and Analogues

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