Olefinic adds epoxides

Several peroxy adds are used in the oonversion of olefins into epoxides. Their properties and pr tarations have been described by Swern, -Included among them are perfbrmio add, peracetic add, perbenxoio acid, monoperphthalic add, and percamphorio acid. More recently irifluoroperacetic acid hsa attained some prominence. Certain desirable features have been discovered in p-nitroperbenzoic add aa well. ... 

Epoxidation of aldehydes and ketones is the most profound utility of the Corey-Chaykovsky reaction. As noted in section 1.1.1, for an a,P-unsaturated carbonyl compound, 1 adds preferentially to the olefin to provide the cyclopropane derivative. On the other hand, the more reactive 2 generally undergoes the methylene transfer to the carbonyl, giving rise to the corresponding epoxide. For instance, treatment of P-ionone (26) with 2, derived from trimethylsulfonium chloride and NaOH in the presence of a phase-transfer catalyst Et4BnNCl, gave rise to vinyl epoxide 27 exclusively. ... 

By analogy to simple olefins, we propose that 0(3P) initially adds to the 1,4 or 1,2 double bonds in polybutadienes at ambient temperature. Since the rate constants for 0(3P) addition to cis-2-butene and 1-butene (as models for 1,4 and 1,2 double bonds, respectively) are in the ratio 4.2 1 at 298 K ( 6), preferential addition to the 1,4 double bonds is assumed to persist to very high vinyl contents (-8011). The biradical adducts then rearrange to epoxides and carbonyl compounds or give rise to chain rupture and/or crosslinking as a consequence of PIF, according to the scheme ... 

Similar to usual olefins, Cjq imdergoes osmylations, epoxidations, and additions of Lewis adds (see Chapter 9). Here, Cjq acts as electron-donating spedes (Scheme 14.5). 

Hickinbottom and co-workere have recently published evident, casting doubt on earlier beliefs that epoxides were intermediates in 11nformation of carbonyl compounds during olefin oxidation by chroma add. For example, 2-methyl-l, 1 diphenyl 1 -propene (Eq. Ill) gave-good yiold of the corresponding epoxide in acetic anhydride along wii-1. 

Other tetrasnhstituted olefins (Eq. 115) have recently boon reported18 4-1844 to yield the corresponding epoxides on oxidation with chromic noid in glacial acetic add, Mosher and co-workers also noted in addition the formation of significant proportions of cyclic carbonate when all traces of winter were excluded from tfio reaction medium by addition of acetic anhydride.1944... 

Optically active diisopinocamphenylborane can be used to resolve racemic olefins. The reagent adds to one enantiomer, and the other is unchanged. Optical purities on the order of 37-65% are possible. Chiral ally lie alcohols can be resolved with chiral epoxidizing agents derived from tartrate complexes of titanium. One enantiomer is epoxidized and the other is not. Thus, die two alcohol enantiomers can be separated, one as the unsaturated alcohol and one as the epoxy alcohol. Use of die other tartrate isomer reverses die stereoselectivity. Selectivities on die order of >100 are possible with this method. As in any kinetic resolution, however, only one enantiomer can be recovered. The other is converted to a different chiral product. 

Free-radical autoxidation of aldehydes with 02 is facile and affords the corresponding peradds, which are used as oxidants for carbonyl compounds. The peracid can transfer an oxygen atom to a substrate such as an olefin or ketone, resulting in the formation of one equivalent of epoxide or ester and add as a co-produd in the absence of metal catalysts [59]. Kaneda and coworkers have developed several HT materials that are active for heterogeneous Baeyer-Villiger reactions with 02/aldehyde [60]. Combination with Lewis addic metals improved the reaction by allowing coordination of the peracid and the intermediate. 

A third one-step addition reaction to C=C double bonds that forms three-membered rings is the epoxidation of olefins with percarboxylic acids (Figure 3.14). Suitable percarboxylic acids must, however, not be (too) explosive. Thus, aromatic percarboxylic adds are preferable. Until recently one epoxidized almost exclusively with mefa-chloroper-benzoic acid (MCPBA). An alternative has become magnesium monoperoxyphthalate (MMPP). In the transition state of this type of epoxidation, four electron pairs are shifted simultaneously (which is a record in this book except for the Corey-Winter elimination in Figure 4.42). 

Peracid methods are a popular choice for hydroxylation of olefins and generally more forcing conditions are required compared with epoxidation. Performic and peracetic acids are usually employed. A convenient and efficient method is to dissolve the olefin in an excess of the carboxylic acid and to slowly add the hydrogen peroxide to the mixture.113 When formic acid is employed, the acidity is usually sufficient to effect hydroxylation via the hydroxyformate (Figure 3.24). 

The fascinating carbenoid character of the epoxide anion is also manifested in an intramolecular cyclopropanation reaction, in which the anion adds across a tethered olefin to provide bicyclo[3.1.0]hexanols (Equation 52). The reaction is remarkably chemo- and diastereoselective. No C-H insertion is observed, and yields are generally very good. The stereochemical outcome is rationalized on the basis of a /ra r-lithiation, as well as the geometric constraints imposed by the [3.1.0] bicyclic system <2004JA8664>. 

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