Methyltrioxorhenium (MTO) catalysis in the epoxidation of alkenes: a synthetic overview

Epoxides are biologically important moiety that is also used as synthetic intermediates. This review aims to present the up-to-date advancements in methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes using diverse oxidizing agents.

Chemo-enzymatic oxidative cleavage of isosafrole for the synthesis of piperonal

Piperonal is a key feedstock for the fine chemical industry. A novel process for its production from isosafrole is described, based on lipase-mediated perhydrolysis in flow, followed by batch alkaline treatment and by MnO2 oxidation in flow.

The Potential Transformation Mechanisms of the Marker Components of Schizonepetae Spica and Its Charred Product

Schizonepetae Spica (SS) is commonly used for treating colds, fevers, bloody stool and metrorrhagia in China. To treat colds and fevers, traditional Chinese medicine doctors often use raw SS, while to treat bloody stool and metrorrhagia, they usually use Schizonepetae Spica Carbonisata (SSC; raw SS processed by stir-frying until carbonization). However, there have been limited investigations designed to uncover the mechanism of stir-fry processing. In the present study, a method combining gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) was developed for the comprehensive analysis of the chemical profiles of SS and SSC samples. Principal component analysis of the GC-MS data demonstrated that there were 16 significant differences in volatile compounds between the SS and SSC samples. The simultaneous quantification of six nonvolatile compounds was also established based on HPLC, and remarkable differences were found between the two products. These changes were probably responsible for the various pharmacological effects of SS and SSC as well as the observed hepatotoxicity. Finally, the mechanisms could be rationalized by deducing possible reactions involved in the transformation of these marker components. This work reports a new strategy to reveal the chemical transformation of SS during stir-fry processing.

Total synthesis of bryostatin 3

Bryostatins are a family of 21 complex marine natural products with a wide range of potent biological activities. Among all the 21 bryostatins, bryostatin 3 is structurally the most complex. Whereas nine total syntheses of bryostatins have been achieved to date, bryostatin 3 has only been targeted once and required the highest number of steps to synthesize (43 steps in the longest linear sequence and 88 total steps). Here, we report a concise total synthesis of bryostatin 3 using 22 steps in the longest linear sequence and 31 total steps through a highly convergent synthetic plan by the use of highly atom-economical and chemoselective transformations in which alkynes played a major role in reducing step count.

Tailoring chemoenzymatic oxidation via in situ peracids

Epoxidation chemistry often suffers from the challenging handling of peracids and thus requires in situ preparation. Here, we describe a two-phase enzymatic system that allows the effective generation of peracids and directly translate their activity to the epoxidation of olefins. We demonstrate the approach by application to lipid and olefin epoxidation as well as sulfide oxidation. These methods offer useful applications to synthetic modifications and scalable green processes.

Catalytic Oxidation Processes for the Upgrading of Terpenes: State-of-the-Art and Future Trends

Terpenic olefins constitute a relevant platform of renewable molecules, which could be used as key intermediates for the perfumery, flavoring, and pharmaceutical industries. The upgrading of these cheap and available agro-resources through catalytic oxidation processes remains of great interest, leading to the formation of either epoxides via the oxidation of the olefinic bond or α,β-unsaturated ketones by the Csp3-H functionalization at the α-position of the double bond. This critical review summarizes some of the most relevant homogeneous or heterogeneous catalysts designed for the oxidation of some abundant terpenic olefins in the last decade (2008–2018).

Efficient and selective oxidation of sulfides in batch and continuous flow using styrene-based polymer immobilised ionic liquid phase supported peroxotungstates

Good conversion and high selectivity for sulfoxidation have been achieved under segmented and continuous flow using a polystyrene-based polymer immobilised ionic liquid phase (PIILP) peroxotungstate.

Ultrasound promoted green oxidation of alkenes with hydrogen peroxide in the presence of iron porphyrins supported on multi-walled carbon nanotubes

In the present work, oxidation of alkenes with hydrogen peroxide in the presence of meso-tetrakis(4-hydroxyphenyl)porphyrinatoiron(III) chloride supported onto surface of functionalized multi-wall carbon nanotubes (FMWCNT), [ Fe ( THPP ) Cl@MWCNT ], is reported. The simple heterogeneous catalyst was characterized by FT-IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and also thermal analysis. The amount of the catalyst loaded on the nanotubes was determined by atomic absorption spectroscopy. This heterogeneous catalyst proved to be an efficient and green catalyst and was successfully able to activate hydrogen peroxide without any additive toward the oxidation of alkenes in ethanol as a green solvent. Performance of the catalyst in oxidation of various alkenes was inspected under reflux, ultrasonic irradiation and mechanical stirring. Moreover, the catalyst can be reused several times under similar conditions.

Composites of [γ-H2PV2W10O40]3− and [α-SiW12O40]4− supported on Fe2O3 as heterogeneous catalysts for selective oxidation with aqueous hydrogen peroxide

The titled heterogeneous catalysts showed high performance for selective oxidation with H₂O₂.

Selective oxidation reactions of natural compounds with hydrogen peroxide mediated by methyltrioxorhenium

We have investigated the oxidative behaviour of natural compounds such as methyl abietate (1), farnesyl acetate (2), α-ionone (3), β-ionone (4), methyl linolelaidate (5), methyl linolenate (6) and bergamottin (7) with the oxidant system methyltrioxo-rhenium/H₂O₂/pyridine. The reactions, performed in CH₂Cl₂/H₂O at 25 °C, have shown good regio- and stereoselectivity. The oxidation products were isolated by HPLC or silica gel chromatography and characterized by MS(EI), ¹H-, ¹³C-NMR, APT, gCOSY, HSQC, TOCSY and NOESY measurements. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects.