Enantioselective Epoxidation of β,β-Disubstituted Enamides with a Manganese Catalyst and Aqueous Hydrogen Peroxide

Clarasó, Carlota; Vicens, Laia; Polo, A.; Costas, Miguel

doi:10.1021/acs.orglett.9b00729

Cited by 20 publications

(13 citation statements)

References 62 publications

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“…Manipulation of the other pyridine had a lower influence: neither the replacement of triisopropylsilyl (TIPS) group with a less‐hindered trimethylsilyl one (TMS, CR,TMS Mn , entry 3) nor with an electron‐rich pyridine ( CR,DMM Mn , entry 4) provided significant changes. As expected, [10b–f] the use of a stronger electron‐donating substituent ( CR,Me2N Mn , entry 5) increased the ee , although at the expense of the yield. Replacement of the pyridine with a benzimidazole ring ( Bz,CR Mn , entry 6) provided modest results.…”

Section: Resultssupporting

confidence: 69%

Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst

2021

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Precise delivery of a proton plays a key role in O 2 activation at iron oxygenases, enabling the crucial OÀ O cleavage step that generates the oxidizing high-valent metaloxo species. Such a proton is delivered by acidic residues that may either directly bind the iron center or lie in its second coordination sphere. Herein, a supramolecular strategy for enzyme-like H 2 O 2 activation at a biologically inspired manganese catalyst, with a nearly stoichiometric amount (1-1.5 equiv) of a carboxylic acid is disclosed. Key for this strategy is the incorporation of an α,ω-amino acid in the second coordination sphere of a chiral catalyst via remote ammonium-crown ether recognition. The properly positioned carboxylic acid function enables effective activation of hydrogen peroxide, leading to catalytic asymmetric epoxidation. Modulation of both amino acid and catalyst structure can tune the efficiency and the enantioselectivity of the reaction, and a study on the oxidative degradation pathway of the system is presented.

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Section: Resultssupporting

confidence: 69%

Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst

2021

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“…The simplest member of the cis -α series, Fe(men), actually also undergoes rapid degradation, presumably because the high ligand flexibility facilitates ligand detachment . However, rigidification of the diamine backbone by encompassing this motif into a cyclic or bicyclic structure (Figure B) increases catalyst stability and significantly improves catalytic activity. − Moreover, these diamine structures insert chirality into the catalyst structure, enabling enantioselective oxidations (the optimal diamine structures are substrate dependent). Finally, these systems have a C 2 symmetry, which makes their structural manipulation straightforward .…”

Section: Principles Of Rational Catalyst Designmentioning

confidence: 99%

Rational Design of Bioinspired Catalysts for Selective Oxidations

2020

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Recognizing Nature’s unique ability to perform challenging oxygenation reactions with exquisite selectivity parameters at iron-dependent oxygenases, chemists have long sought to understand and mimic these enzymatic processes with artificial systems. In the last two decades, replication of the reactivity of non-heme iron oxygenases has become feasible even with simple coordination complexes of iron and manganese. A bona fide minimalistic functional model was the tetradentate-N4 ligand based iron complex [Fe(tpa)(CH3CN)2]2+(Fe(tpa), tpa = tris(2-methylpyridyl)amine), which activates H2O2 via a mechanism that mirrors key steps of enzymatic O2 activation processes at mononuclear iron centers: controlled O–O bond cleavage, generation of a high-valent FeO oxidant, and promotion of almost the full spectrum of its oxidative reactivity (C–H hydroxylation, olefin epoxidation, syn-dihydroxylation, and desaturation). These landmark discoveries set the mechanistic framework to use iron coordination complexes with nitrogen-rich ligands as catalysts for oxidizing organic substrates under synthetically relevant conditions. Due to proof-of-concept demonstrations of the potential of these catalysts in organic synthesis, this chemistry has flourished over the past decade. In parallel to the realization of the potential of this class of catalysts in diverse organic transformations, effort has been spent to manipulate the catalyst structure with the aim of tuning both the reactivity and selectivity of the oxidation reactions. This perspective provides an overview of the progress of this research. Some key features of the archetypical Fe(tpa) catalyst have stayed surprisingly true throughout this evolution, but a series of alterations that modulate its electronic, steric, or binding properties allowed a rational elicitation of a specific reactivity or selectivity. In some cases, the replacement of iron by manganese has also proven beneficial. Overall, the rational optimization of the catalyst structure has enabled the development of highly asymmetric olefin epoxidation, syn-dihydroxylation, and site-selective and even enantioselective C–H oxidation reactions.

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“…Epoxidation of β,β-disubstituted enamides has been considered as a difficult task and the research group of Costas designed a chiral manganese catalyst, [(S,S)-Me 2 NOhq-Mn] (Ohq = 1,1',2,2',3,3',4,4'-octahydro-1,4'-biisoquinoline) in this regard in 2019. [25] This Mncomplex facilitated epoxidation with H 2 O 2 and carboxylic acid under milder reaction conditions in short reaction time accompanying high enantioselectivity and moderate to excellent yields (Scheme 7). Increase in the size of alkyl groups at the N-alkyl position showed direct increase in enantioselectivity.…”

Section: Scheme 2 Enantioselective Epoxidation Of Terminal Alkenes Wmentioning

confidence: 99%

Recent Trends and Prospects in Homogeneous Manganese‐Catalysed Epoxidation

et al. 2021

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Epoxidation of alkenes is a significant reaction in organic chemistry due to its opportunities in producing compounds of biochemical interest. Catalytic epoxidation with first‐row transition elements has gained attention in the latest years wherein manganese based catalysts stand superior by satisfying numerous principles of green chemistry. In this review, we have summarized the recent developments in olefin epoxidation using homogeneous manganese catalysts. Manganese complexes with porphyrin, Schiff base, salen, and other non‐heme ligands made efficient catalytic systems during the last five years. Notably, we witnessed greener approaches in recent reports wherein photo‐catalysis is a promising strategy. We anticipate that the review will benefit the researchers to get a better understanding of the reaction and to choose the best catalysts for their reactions.

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Enantioselective Epoxidation of β,β-Disubstituted Enamides with a Manganese Catalyst and Aqueous Hydrogen Peroxide

Abstract: Enantioselective epoxidation of β,β-disubstituted enamides with aqueous hydrogen peroxide and a novel manganese catalyst is described. Epoxidation is stereospecific and proceeds fast under mild conditions. Amides are disclosed as key functional groups to enable high enantioselectivity.

Cited by 20 publications

References 62 publications

Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst

Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst

Rational Design of Bioinspired Catalysts for Selective Oxidations

Recent Trends and Prospects in Homogeneous Manganese‐Catalysed Epoxidation

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