Diastereoselective epoxidation of olefins by organo sulfonic peracids, II

Enantioselective Flow Synthesis of Rolipram Enabled by a Telescoped Asymmetric Conjugate Addition-Oxidative Aldehyde Esterification Sequence Using in Situ-Generated Persulfuric Acid as Oxidant

A novel approach is reported for the enantioselective flow synthesis of rolipram comprising a telescoped asymmetric conjugate addition-oxidative aldehyde esterification sequence followed by trichlorosilane-mediated nitro group reduction and concomitant lactamization. The telescoped process takes advantage of a polystyrene-supported chiral organocatalyst along with in situ-generated persulfuric acid as a robust and scalable oxidant for direct aldehyde esterification. This approach demonstrates significantly improved productivity compared with earlier methodologies while ensuring environmentally benign metal-free conditions.

SO2F2-Mediated Epoxidation of Olefins with Hydrogen Peroxide

An inexpensive, mild, and highly efficient epoxidation protocol has been developed involving bubbling SO₂F₂ gas into a solution of olefin, 30% aqueous hydrogen peroxide, and 4 N aqueous potassium carbonate in 1,4-dioxane at room temperature for 1 h with the formation of the corresponding epoxides in good to excellent yields. The novel SO₂F₂/H₂O₂/K₂CO₃ epoxidizing system is suitable to a variety of olefinic substrates including electron-rich and electron-deficient ones.

The Reactions of (+)-2- and (+)-3-Carenes with the Retention of the Bicyclic Framework

Carane-type compounds have attracted attention in recent years due to their practical importance. This review is focused on describing the developments in the synthesis of trimethylbicyclo[4.1.0]heptanes and their unsaturated analogues from monoterpenes (+)-2- and (+)-3-carenes published mostly during the last decade.

Rapid ultrasensitive measurement of salivary cortisol using nano-linker chemistry coupled with surface plasmon resonance detection

Cortisol detection in saliva is of great interest for the diagnosis of various disease states and the monitoring of stress in humans. Currently, measurements are performed predominantly by radioimmunoassay (RIA) which is expensive, labour intensive, uses hazardous radioisotopes and involves extensive delays in obtaining results. A rationally designed cortisol-linker conjugate allowing high assay sensitivity was employed as a coating antigen in a microfluidic surface plasmon resonance (SPR) biosensor immunoassay for the ultrasensitive and rapid detection of salivary cortisol. Detection of cortisol is by competitive immunoassay using a secondary antibody for signal enhancement. The method requires no chemical extraction or complex sample pre-treatment despite high saliva viscosity. The cortisol assay was optimized for maximum sensitivity in buffer before being adapted for the salivary matrix, where it showed a limit of detection of 49 pg/mL. The results showed good correlation to RIA (r = 0.94). The biosensor assays showed an inter-assay coefficient of variation (CV) of 13.5% and recoveries close to 100%. The covalently immobilized sensor surface provided stable responses for more than 140 binding and regeneration cycles, enabling re-use. Cortisol in saliva was detected across the physiologically relevant range using the SPR immunobiosensor by employing a rationally designed assay format including signal enhancement for maximum sensitivity. The system can handle saliva matrix effects by use of chemical treatment during the assay to reduce non-specific binding to sensor surfaces. This sensor system provides an automated, high sensitivity analytical tool capable of yielding results in approximately 15 min. This biosensor could potentially be used for active stress-monitoring and in the diagnosis of disease.

Ultrasound assisted phase-transfer catalytic epoxidation of 1,7-octadiene - a kinetic study

An ultrasound assisted phase-transfer catalyzed epoxidation of 1,7-octadiene is greatly enhanced by using a cocatalyst of phosphotungstic acid in the presence of hydrogen peroxide in an organic solvent/aqueous solution two-phase medium. An active intermediate of the catalyst (Q3PW12(O)nO40, where Q = R4N+) produced from the reaction of phosphotungstic acid, hydrogen peroxide, and Aliquat 336. A rational mechanism of epoxidation is proposed to account for the reaction from the experimental evidence. The organic-phase reactions, including two series reactions, are the rate-controlling steps to produce two products, viz., 1,2-epoxy-7-octene and 1,2,7,8-diepoxyoctane. The kinetics of epoxidation, including the characteristics of the catalyst and the effect of the amount of cocatalyst, agitation speed, quaternary ammonium salts, amount of Aliquat 336, amount of hydrogen peroxide, amount of chloroform, pH value, organic solvents, and temperature on the conversion of 1,7-octadiene were investigated in detail. A kinetic model was built, from which a pseudo-first-order rate law is sufficient to describe the behavior of the reaction.

Regio and stereoselective oxidations of unsaturated steroidal compounds with H2O2 mediated by CH3ReO3

We have investigated the oxidative behavior of sterols such as cholesteryl acetate (1), 7-dehydrocholesteryl acetate (2), ergosteryl acetate (3), cholecalciferol acetate (Vitamin D(3) acetate) (4) and ergocalciferol acetate (Vitamin D(2) acetate) (5) with the oxidant system methyltrioxorhenium/H(2)O(2)/pyridine in order to check potential parameters controlling the selectivity. The reactions, performed in CH(2)Cl(2)/H(2)O at 25 degrees C, have shown good regio- and stereoselectivity. All oxidation products were isolated by high-performance liquid chromatography (HPLC) and characterized by MS(EI) or FAB, (1)H NMR, (13)C NMR, APT, COSY, HSQC, HMBC, ROESY and NOEDS measurements. Seven new oxygenated compounds were also obtained. Under the experimental conditions adopted in this work, only the diene steroids, i.e. 7-dehydrocholesteryl acetate and ergosteryl acetate, undergo hydrolytic oxirane ring opening, whereas Vitamin D(2) and D(3) acetates, containing the triene system and cholesteryl acetate yield only epoxides. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects.

Highly regioselective and diastereoselective epoxidation of allylic amines with Oxone

Allylic amines (as their protonated ammonium salts) can be epoxidised with high syn diastereoselectivity and regioselectivity at the proximal alkene in substrates with several double bonds using Oxone. The protonated ammonium cation activates the Oxone by hydrogen bonding, thus promoting the oxidation of groups within the vicinity of the complex.

Synthesis of cryptophycin 52 using the Shi epoxidation

[reaction: see text] A synthesis of cryptophycin 52 is reported using a Shi epoxidation strategy to install the epoxide moiety in a diastereoselective fashion. Several epoxidation results for cryptophycin substrates are disclosed followed by a discussion of the details relating to the preparation of cryptophycin 52 in two synthetic steps from one of the intermediate epoxides.

Highly beta-selective epoxidation of delta5-unsaturated steroids catalyzed by ketones

A general catalytic and environmentally friendly method for beta-epoxidation of delta5-unsaturated steroids has been developed, which uses ketones as the catalysts and Oxone as the terminal oxidant. A whole range of delta5-unsaturated steroids, which bear different functional groups such as hydroxyl, carbonyl, acetyl, or ketal, as well as different side chains, were conveniently converted to the corresponding synthetically and biologically interesting 5beta,5beta-epoxides with excellent beta-selectivities and high yields.

Epoxidation of acyclic chiral allylic alcohols with peroxy acids: spiro or planar butterfly transition structures? A computational DFT answer

The mechanism of the epoxidation of two chiral allylic alcohols, i.e., 3-methyl-3-buten-2-ol and (Z)-3-penten-2-ol, with peroxyformic acid has been investigated by locating 20 transition structures with the B3LYP/6-31G* method and by evaluating their electronic energy also at the B3LYP/6-311+G**@B3LYP/6-31G* theory level. Relative stability of TSs, as far as electronic energy is concerned, is basis set dependent; moreover, it also depends on entropy and solvent effects. Free enthalpies, calculated by using electronic energy at the higher theory level and with inclusion of solvent effects, indicates that syn, exo TSs, where the olefinic OH group hydrogen bonds the peroxy oxygens of the peroxy acid, outweigh syn, endo TSs, where the peroxy acid carbonyl oxygen is involved in hydrogen bonding. In the former TSs the peroxy acid moiety maintains its planar geometry while in the latter ones a strong out-of-plane distortion of peroxy acid is observed. This distortion makes it viable an unprecedented 1,2-H shift, as a possible alternative to the 1,4-H shift, for the peroxy acid hydrogen. In fact, for one syn, endo TS IRC analysis demonstrated that the 1,2-H shift mechanism is actually operative. The geometry of all TSs substantially conforms to a spiro (i.e., with the peroxy acid plane almost perpendicular to the C=C bond axis) butterfly orientation of the reactants while no TS resembles, even loosely, the planar butterfly structure. Theoretical threo/erythro epoxide ratios are in fair accord with experimental data. Calculations indicate that threo epoxides derive mostly from TSs in which the olefinic OH assumes an outside conformation while erythro epoxides originate from TSs with the OH group in an inside position. Computational findings do not support the qualitative TS models recently proposed for these reactions.

Diastereoselective Epoxidation of Cyclohexene Derivatives by Dioxiranes Generated in Situ. Importance of Steric and Field Effects

In this paper, diastereoselective epoxidation of substituted cyclohexenes (substrates 1-7) by dioxiranes generated in situ from ketones and Oxone was systematically investigated. The results revealed that the diastereoselectivity was determined by the steric and field effects of both dioxiranes and substrates, and high diastereoselectivity can be achieved by tuning the ketone structure. Among the ketones tested, 12 and 19 gave the best diastereoselectivities.

Organo Sulfonic Peracids. 4.(1) The Reaction of Arenesulfonylimidazoles with H(2)O(2) in the Presence of Ketones. A New Entry to Dioxiranes

The reaction of ketones (acetone, 1,1,1-trifluoropropan-2-one) with the oxidation system (arenesulfonyl)imidazole (2)/H(2)O(2)/NaOH permits the in situ generation of the corresponding dimethyl- and methyl(trifluoromethyl)dioxirane in various solvents. This has been established by the chemoselective oxidation of azomethines 6, the diastereoselective oxidation of cholesterol (12), and (18)O-labeling experiments. Because only 5 equiv of ketone are used, the dioxirane oxidation pathway appears to be virtually exclusive one in this system. One example for the nonaqueous in situ generation of dimethyldioxirane (1a) is given.