Epoxides commercially available

Miscellaneous Epoxide Resins 765 Table 26.6 Some commercially available cyclic-aliphatic epoxide resins... 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

A detailed procedure for the use of MCPBA recently appeared in Reagents for Organic Synthesis by Fieser and Fieser. The commercially available MCPBA (Aldrich) is 85% pure the contaminant, m-chlorobenzoic acid, can be removed by washing with a phosphate buffer of pH 7.5. The epoxidation is usually performed as follows a solution of 3 -acetoxy-5a-androst-16-ene (2.06 g, 6.53 mmoles) in 25 ml of chloroform (or methylene dichloride) is chilled to 0° in a flask fitted with a condenser and drierite tube and treated with a solution of commercial MCPBA (1.74 g, 20% excess) in 25 ml chloroform precooled to the same temperature. The mixture is stirred and allowed to warm to room temperature. After 23 hr (or until TLC shows reaction is complete) the solution is diluted with 100 ml chloroform and washed in sequence with 100 ml of 10% sodium sulfite or sodium iodide followed by sodium thiosulfate, 200 ml of 1 M sodium bicarbonate and 200 ml water. The chloroform extract is dried (MgS04) and evaporated in vacuo to a volume of ca. 10 ml. Addition of methanol (10 ml) followed by cooling of the mixture to —10° yields 0.8 gof 16a,17a-epoxide mp 109.5-110°. Additional product can be obtained by concentration of the mother liquor (total yield 80-90%). 

Epoxidation of the A -enol acetate was originally carried out with per-benzoic acid. Monoperphthalic acid has also been used, but is apparently more susceptible to steric and conformational factors. The commercially available peracetic acid is generally most convenient. Based on the expected backside attack, the derived epoxides have the 17a configuration, and hydrolysis always produces the 17a-hydroxy group. 

In order to obtain good yields, it is important to use dry solvent and reagents. The commercially available t-butyl hydroperoxide contains about 30% water for stabilization. For the use in a Sharpless epoxidation reaction the water has to be removed first. The effect of water present in the reaction mixture has for example been investigated by Sharpless et al. for the epoxidation of (E)-a-phenylcinnamyl alcohol, the addition of one equivalent of water led to a decrease in enantioselectivity from 99% e.e. to 48% e.e. 

Replacement of the carbamate function by an amide seems to be compatible with meprobamate-like activity in a compound formally derived from a 1,2-glycol. Oxidation of the commercially available aldehyde, 22, under controlled conditions affords the corresponding acid (23). This is then converted to its amide (24) via the acid chloride. Epoxidation by means of perphthalic acid affords oxanamide (25). ... 

A retrosynthetic analysis of fragment 152 can be completed through cleavage of the C16-C17 bond in enone 155, the projected precursor of epoxide 152. This retrosynthetic maneuver furnishes intermediates 156 and 157 as potential building blocks. In the forward sense, acylation of a vinyl metal species derived from 156 with Weinreb amide 157 could accomplish the construction of enone 155. Iodide 153, on the other hand, can be traced retrosynthetically to the commercially available, optically active building block methyl (S)-(+)-3-hydroxy-2-methyIpropionate (154). 

The optically active iodide 153 (Scheme 43) can be conveniently prepared from commercially available methyl (S)-(+)-3-hydroxy-2-methylpropionate (154) (see Scheme 41). At this stage of the synthesis, our plan called for the conversion of 153 to a nucleophilic organometallic species, with the hope that the latter would combine with epoxide 152. As matters transpired, we found that the mixed higher order cuprate reagent derived from 153 reacts in the desired and expected way with epoxide 152, affording alcohol 180 in 88% yield this regioselective union creates the C12-C13 bond of rapamycin. 

Finally, the necessity arose for the synthesis of pentulose 21, labeled with, 3C on the central carbons, C-2 and C-3, for an independent biosynthetic study, which is reported in Section III.5.27 The doubly labeled ester 34 (Scheme 14) is readily available by a Wittig- Homer condensation of benzyloxyacetaldehyde with commercially available triethylphosphono-(l,2-l3C2)acetate. Chirality was introduced by the reduction of ester 34 to the allylic alcohol, which produced the chiral epoxide 35 by the Sharpless epoxidation procedure. This was converted into the tetrose 36, and thence, into the protected pentulose 37 by the usual sequence of Grignard reaction and oxidation. 

Many other reagents for converting alkenes to epoxides,including H2O2 and Oxone , VO(0-isopropyl)3 in liquid C02, ° polymer-supported cobalt (II) acetate and 02, ° and dimethyl dioxirane.This reagent is rather versatile, and converts methylene oxiranes to spiro-epoxides. ° ° One problem with dimethyloxirane is C—H insertion reactions rather than epoxidation. Magnesium monoperoxyphthalate is commercially available, and has been shown to be a good substitute for m-chloroperoxybenzoic acid in a number of reactions. 

In the present study the dimer (salen)CoAlX3 showed enhanced activity and enantioselectivity. The catalyst can be synthesized easily by readily commercially available precatalyst Co(salen) in both enantiomeric forms. Potentially, the catalyst may be used on an industrial scale and could be recycled. Currently we are looking for the applicability of the catalyst to asymmetric reaction of terminal and meso epoxides with other nucleophiles and related electrophile-nucleophile reactions. 

Chiral and achiral Jacobsen s catalysts exhibit similar diatereomeric excesses during the diastereoselective epoxidation of R-(+)-limonene using in situ prepared oxidizing agents. Therefore, the chiral center of the substrate appears to govern the chiral induction. In contrast, the chirality of the Jacobsen s catalyst appears to be responsible for the chiral induction when commercially available oxidants were used. 

The location of the position of double bonds in alkenes or similar compounds is a difficult process when only very small amounts of sample are available [712,713]. Hass spectrometry is often unsuited for this purpose unless the position of the double bond is fixed by derivatization. Oxidation of the double bond to either an ozonide or cis-diol, or formation of a methoxy or epoxide derivative, can be carried out on micrograms to nanograms of sample [713-716]. Single peaks can be trapped in a cooled section of a capillary tube and derivatized within the trap for reinjection. Ozonolysis is simple to carry out and occurs sufficiently rapidly that reaction temperatures of -70 C are common [436,705,707,713-717]. Several micro-ozonolysis. apparatuses are commercially available or can be readily assembled in the laboratory using standard equipment and a Tesla coil (vacuum tester) to generate the ozone. Reaction yields of ozonolysis products are typically 70 to 95t, although structures such as... 

An important factor in all these experiments is the choice of bead used to immobilize the probe. Biochemists have considered cross-linked agarose beads to be exceptionally hydrophilic with a low tendency to bind proteins nonspecifically, and these beads have the further attraction of being commercially available in activated forms (succinimidyl esters, epoxides, and maleimides, for example). However, early trials of bead-based chemical proteomics have shown that many proteins in mammalian cell lysates bind tenaciously to agarose beads. This was unimportant in many studies in which protein-protein interactions were detected by coimmunoprecipitation with immunochemical... 

Biocatalytic hydrolysis or transesterification of esters is one of the most widely used enzyme-catalyzed reactions. In addition to the kinetic resolution of common esters or amides, attention is also directed toward the reactions of other functional groups such as nitriles, epoxides, and glycosides. It is easy to run these reactions without the need for cofactors, and the commercial availability of many enzymes makes this area quite popular in the laboratory. 

In summary, the formation of optically active compounds through hydrolysis reactions is dominated by biocatalysis mainly due to the availability and ease of use of a wide variety of esterases, lipases and (to a lesser extent) acylases. Epoxide ring-opening (and related reactions) is likely to be dominated by salen-metal catalysts while enzyme-catalysed nitrile hydrolysis seems destined to remain under-exploited until nitrilases or nitrile hydratases become commercially available. 

All of the reagents required for the asymmetric epoxidation are commercially available. 

This method, specific for the epoxidation of allylic alcohols, gives good results if the reaction is carried out under strictly anhydrous conditions, otherwise the yield or the enantiomeric excess can decrease, sometimes dramatically. This can explain the small differences between the results obtained during the validation experiments and the published results. All the different reagents are commercially available they can be used as received but in case of low yield and/or enantiomeric excess they should be distilled and dried under an inert atmosphere. Table 5.1 gives some other examples of substrates which can be epoxidized using the procedure described above. 

To date, the most frequently used ligand for combinatorial approaches to catalyst development have been imine-type ligands. From a synthetic point of view this is logical, since imines are readily accessible from the reaction of aldehydes with primary or secondary amines. Since there are large numbers of aldehydes and amines that are commercially available the synthesis of a variety of imine ligands with different electronic and steric properties is easily achieved. Additionally, catalysts based on imine ligands are useful in a number of different catalytic processes. Libraries of imine ligands have been used in catalysts of the Strecker reaction, the aza-Diels-Alder reaction, diethylzinc addition, epoxidation, carbene insertions, and alkene polymerizations. 

---