Heterogenisation of ketone catalysts within mesoporous supports for asymmetric epoxidation

The synthesis of the first mesoporous silica (150 Å) anchored carbohydrate-derived chiral ketone is described. This new heterogeneous catalyst has been shown to be effective in the asymmetric epoxidation of olefins by oxone. The heterogeneous ketone catalyst has comparable activity to that of its homogeneous counterpart and returned enantioselectivities up to 90% e.e

Enantioselective Synthesis of 5-epi-Citreoviral Using Ruthenium-Catalyzed Asymmetric Ring-Closing Metathesis

Chiral ruthenium olefin metathesis catalysts can perform asymmetric ring-closing reactions in ≥90% ee with low catalyst loadings. To illustrate the practicality of these reactions and the products they form, an enantioselective total synthesis of 5-epi-citreoviral was completed by using an asymmetric ring-closing olefin metathesis reaction as a key step early in the synthesis. All of the stereocenters in the final compound were set by using the chiral center generated by asymmetric olefin metathesis

Recent progress in the synthesis of six-membered aminocyclitols (2008-2017)

Aminocyclitols are of interest as glucosidase inhibitors, as probes for the study of pseudoglycosyltransferases, and as potential therapeutics for the treatment of Gaucher’s disease. The synthesis of these targets was reviewed in early 2008, and the aim of this review is to cover material relevant to the synthesis of aminocyclitols since that time. While not a focus of this review, biological evaluation of compounds will be presented where it is recorded in the literature

Modular polyoxometalate-layered double hydroxides as efficient heterogeneous sulfoxidation and epoxidation catalysts

Selective sulfoxidation of sulfides and epoxidation of olefins are two types of important organic reactions and the corresponding products of sulfoxides, sulfones and epoxides are widely used as raw materials in industrial processes. The fabrication of one efficient catalyst for both reactions, remains a challenging task. In this paper, we report the preparation of a highly efficient heterogeneous catalyst of Mg3Al-ILs-La(PW11)2 using an exfoliation/assembly approach. The catalyst was characterized by FT-IR, XRD, TG/DTA, BET, XPS, 29Si CP/MAS NMR, the 27Al-MAS NMR, SEM, HRTEM, EDX etc. The designed catalyst showed high efficiency and selectivity for sulfoxidation of sulphides and epoxidation of olefins under mild conditions at a production rate of 208 mmol g-1 h-1 and 31 mmol g-1 h-1, respectively. Moreover, the Mg3Al-ILs-La(PW11)2 can be recycled and reused at least 5 times without obvious decrease of its catalytic activity. The scaled-up experiments revealed that the catalyst retained its efficiency and robustness, demonstrating the catalyts' great potential for industrial applications

Unraveling the mechanism of the manganese-salen epoxidation

Chiral salen-type complexes are valuable catalysts for the antioselective epoxidation of unfunctionlized olefins. The mechanism of this reaction with the manganese-salen complex has always been the subject of an intense debate [1, 2]. The originally proposed mechanism featuring a radical intermediate seems to fail in explaining several experimental observations[3] and various alternatives have been proposed. However the obtained results were highly dependent of the chosen methodology. We will present a methodological study comparing a broad range of DFT functionals with high-level CASSCF calculations [4]. An OPBE functional was shown to be the most performant. Using this functional it is confirmed that the mechanism featuring a radical intermediate is indeed the most likely. Moreover it makes it possible to explain the experimental observations that did not fit in the classical model. For example olefins with a cyclopropane moiety next to the double bound result in a mixture of epoxides and ringopening products depending on the exact reaction conditions. Our calculations show that a radical reaction intermediate can lead to the observed product distribution. This methodology can thus prove to give more insights in the mechanism of this interesting catalyst, allowing it to be optimized further for numerous applications

Synthetic applications of chiral unsaturated epoxy alcohols prepared by sharpless asymmetric epoxidation

An overview of the synthesis and applications of chiral 2,3-epoxy alcohols containing unsaturated chains is presented. One of the fundamental synthetic routes to these compounds is Sharpless asymmetric epoxidation, which is reliable, highly chemoselective and enables easy prediction of the product enantioselectivity. Thus, unsaturated epoxy alcohols are readily obtained by selective oxidation of the allylic double bond in the presence of other carbon-carbon double or triple bonds. The wide availability of epoxy alcohols with unsaturated chains, the versatility of the epoxy alcohol functionality (e.g. regio- and stereo-selective ring opening; oxidation; and reduction), and the arsenal of established alkene chemistries, make unsaturated epoxy alcohols powerful starting materials for the synthesis of complex targets such as biologically active molecules. The popularization of ring-closing metathesis has further increased their value, making them excellent precursors to cyclic compounds

Oxidoperoxidomolybdenum(VI) complexes with acylpyrazolonate ligands: synthesis, structure and catalytic properties

Oxidoperoxido–molybdenum(VI) complexes containing acylpyrazolonate ligands were obtained by reaction of [Mo(O)(O)2(H2O)n] with the corresponding acylpyrazolone compounds HQR. Complexes Ph4P[Mo(O)(O2)2(QR)] (R = neopentyl, 1; perfluoroethyl, 2; hexyl, 3; phenyl, 4; naphthyl, 5; methyl, 6; cyclohexyl, 7; ethylcyclopentyl, 8) were obtained if the reaction was carried out with one equivalent of HQR in the presence of Ph4PCl. Alternatively, neutral complexes [Mo(O)(O2)(QR)2] (R = neopentyl, 9; hexyl, 10; cyclohexyl, 11) were formed when two equivalents of HQR were used in the reaction. These complexes were isolated in good yields as yellow or yellow-orange crystalline solids and were spectroscopically (IR, 1H, 13C{1H} and 31P{1H} NMR), theoretically (DFT) and structurally characterised (X-ray for 1, 2, 9 and 10). Compounds 1 and 9 were selected to investigate their catalytic behaviour in epoxidation of selected alkenes and oxidation of selected sulphides, while 10 and 11 were tested as catalyst precursors in the deoxygenation of selected epoxide substrates to alkenes, using PPh3 as the oxygen-acceptor. Complexes Ph4P[Mo(O)(O2)2(QR)] were shown to be poor catalyst precursors in oxidation reactions, while the activity of [Mo(O)(O2)(QR)2] species is good in all the studied reactions and comparable to related oxidoperoxido–molybdenum(VI) complexes. Complex [Mo(O)2(QC6)2], 12, was obtained by treatment of 10 with one equivalent of PPh3, demonstrating that the first step in the epoxide deoxygenation mechanism was the oxygen atom transfer toward the phosphane.Junta de Andalucía (Proyecto de Excelencia, FQM-7079)Universidad de Sevilla (VI Plan Propio

Recent Applications of the Simple Hydrocarbon Cyclooctatetrene as a Starting Material for Complex Molecule Synthesis

Cyclooctatetraene [COT], a simple non-aromatic cyclic polyene, is capable of undergoing a variety of oxidation and cycloaddition reactions to afford polycyclic structures. In addition, complexation of COT or the cycloaddition products with transition metals facilitates bond formation. Recent developments in the reactivity of COT and application to the synthesis of naturally occurring and non-naturally occurring compounds is reviewed

P450BM3-Catalyzed Oxidations Employing Dual Functional Small Molecules

A set of dual functional small molecules (DFSMs) containing different amino acids has been synthesized and employed together with three different variants of the cytochrome P450 monooxygenase P450BM3 from Bacillus megaterium in H2O2-dependent oxidation reactions. These DFSMs enhance P450BM3 activity with hydrogen peroxide as an oxidant, converting these enzymes into formal peroxygenases. This system has been employed for the catalytic epoxidation of styrene and in the sulfoxidation of thioanisole. Various P450BM3 variants have been evaluated in terms of activity and selectivity of the peroxygenase reactions.MINECO-CTQ2016-76908-C2-1,2-PComisión Europea de Investigación-ERC-648026Unión Europea-H2020-BBI-PPP-2015-2-1-720297Organización Holandesa de Investigación Científica (VICI)-724.014.00