Synthetic enzymes. Part 2. Catalytic asymmetric epoxidation by means of polyamino-acids in a triphase system

Juliá, S.; Guixer, Joan; Masana, Jaume; ROCAS, J.; Colonna, Stefano; Annuziata, Rita; Molinari, Henríette

doi:10.1039/p19820001317

Cited by 223 publications

(74 citation statements)

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“…Another main feature in their 1 H and 13 C NMR spectra were the resonances assigned to -H ( = 4.16-4.38 ppm) and C-( = 59.1-60.9 ppm) which appeared at higher frequency than that of -H ( = 3.74-3.80 ppm) and C-( = 58.3-59.0 ppm). The coupling constant 3 J H -H-= 1.6-1.7 Hz of compounds 3a-h were consistent with those of trans-1,2-disubstituted epoxides, this relative configuration was expected for an epoxide obtained from a trans-alkene [41][42][43].…”

Section: J Heterocyclic Chem 43 1319 (2006)mentioning

confidence: 63%

Epoxidation studies of 2-styrylchromones using jacobsen's catalyst and hydrogen peroxide and iodosylbenzene as oxidants

Santos

Silva

Cavaleiro

et al. 2006

Journal of Heterocyclic Chemistry

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The epoxidation of 2‐styrylchromones 2a‐h using Jacobsen's Mn(III)[salen] complex 1 as catalyst is reported for the first time. Several studies were performed using both hydrogen peroxide and iodosylbenzene as oxidants, in order to obtain the α,β‐epoxy‐2‐styrylchromones 3a‐h regioselectively. Due to the low reactivity of the substrates and the highly unstable character of the formed epoxides, reactions should be interrupted at lower conversions to obtain acceptable yields, especially when hydrogen peroxide is used.

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Section: J Heterocyclic Chem 43 1319 (2006)mentioning

confidence: 63%

Epoxidation studies of 2-styrylchromones using jacobsen's catalyst and hydrogen peroxide and iodosylbenzene as oxidants

Santos

Silva

Cavaleiro

et al. 2006

Journal of Heterocyclic Chemistry

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“…Asymmetric variants of this epoxidation with both chiral metal and organic catalysts have also been reported. [8][9][10][11][12][13] It is well-established that the epoxide 3 is formed via a two-step mechanism (Scheme 1); nucleophilic addition of the hydroperoxide 2 to 1 followed by an intramolecular nucleophilic substitution of the resulting enolate (5) that breaks the weak peroxide bond. In principle this epoxidation pathway (1 to 3) could be converted into a peroxidation pathway (1 to 6) if 5 could be trapped by protonation, although the overwhelming preference of 5 for the intramolecular nucleophilic substitution is evident from the lack of reported peroxidation of α,β-unsatrated carbonyl compounds.…”

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confidence: 99%

Catalytic Enantioselective Peroxidation of α,β-Unsaturated Ketones

et al. 2008

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The number of biologically interesting natural products possessing peroxide structure motifs is substantial and still growing. 1 Many peroxy natural products display antitumor, anticancer and anti parasite activities, which are attributed to the propensity of the peroxide to initiate radical reactions in an ironrich environment. 2 Furthermore, peroxide natural products such as artemisinin are clinically important anti malaria drugs. Despite the potential of chiral peroxides as biologically interesting or even clinically important compounds, synthetic methods for the preparation of chiral peroxides are highly limited. 3,4,5,6 In particular efficient catalytic enantioselective peroxidations with simple achiral precursors are urgently needed, yet none are available. In fact only a single example of a chiral auxiliarydirected peroxidation in high diastereoselectivity could be found in the literature. 7 Herein, we wish to report the development of a highly enantioselective peroxidation of α,β-unsaturated ketones with an easily accessible chiral organic catalyst.The base-promoted reaction of α,β-unsaturated ketones 1 with hydroperoxides 2 represents a classic epoxidation reaction. Asymmetric variants of this epoxidation with both chiral metal and organic catalysts have also been reported. 8-13 It is well-established that the epoxide 3 is formed via a two-step mechanism (Scheme 1); nucleophilic addition of the hydroperoxide 2 to 1 followed by an intramolecular nucleophilic substitution of the resulting enolate (5) that breaks the weak peroxide bond. In principle this epoxidation pathway (1 to 3) could be converted into a peroxidation pathway (1 to 6) if 5 could be trapped by protonation, although the overwhelming preference of 5 for the intramolecular nucleophilic substitution is evident from the lack of reported peroxidation of α,β-unsatrated carbonyl compounds.Although chiral amine-catalyzed nucleophilic epoxidations of α,β-unsaturated carbonyl compounds have already been reported, 13 we suspected that a cinchona alkaloid derivative such as 8 14 could not only render the nucleophilic addition of the hydroperoxide 2 to the iminium intermediate 9 enantioselective, but also strongly influence the partitioning of the peroxyenamine intermediate 10 between the epoxidation (10 to 11) and the peroxidation (10 to 12) pathways (Scheme 2). Presumably, due to steric crash and multipoint binding interactions between the peroxyenamine intermediate and the covalently linked cinchona alkaloid, the bond-rotational freedom of the peroxyenamine should be hampered, compared to that of the enolate 5 in Scheme 1. We expected that this conformational rigidity imposed by 8 on the peroxyenamine would diminish its ability to adopt the active conformation by which the nucleophilic enamine moiety is optimally aligned relative to the O-O bond for the nucleophilic attack. This in turn would decelerate the epoxidation. In contrast, with the NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript protonated quinuclidine as a prot...

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“…Asymmetric epoxidations of enones with hydrogen peroxide or alkyl hydroperoxide underchiral phase transfer conditions have been developed by Wynberg,2) Colona 3 ) and Mazaleyrat 4 ). Although the enantiomeric excess (%e.e.…”

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confidence: 99%