Epoxides with periodic acid

The second of the three types of qualitative teste mentioned above involves acid-catalyzcd cleavage of an epoxide with periodic acid.38 The IOf ion then oxidizes the resulting 1,2-diol in the usual manner, while itself undergoing reduction to iodato. In the presence of AgH ion, the gradual formation of iodate will be marked by precipitation of silver iodate (Eq. 983). An obvious drawback to this procedure is that any other functional groups capable of reducing IOf iou will interfere with epoxide detection. 

Alternatively, the cyclobutanones can be made by two-step procedures, i.e. osmium(VIII) oxide oxidation to the diol followed by further oxidation either by lead(IV) acetate 85 or sodium periodate,86,87 or epoxidation followed by oxidation with periodic acid,15,63 are reported to yield the ketones. 

Several analytical procedures are baaed on the hydration rather than hydrohalogenation of epoxide . Tlie resultittg 1,2-diols are assayed by oxidative titration with periodic acid in aqueous sulfurio acid or perchloric acid.4711 Alternatively, carbonyl compounds formed on periodic acid oxidation of 1,2-diola may be determined color imetricajlv wkh phenylbydrwine or other suitable reagents.247 374... 

Polyunsaturated aliphatic alkohols, aldehydes, ketones, and esters occur as fragrance components in fats, oils, fruits and plants 158). As an example the synthesis of ethyl (2 ,4Z)-2,4-decadienoate (232, pear ester ), which is responsible for the aroma of bartlett pears 161) is given. 2,4-Diunsaturated ester 232 may be obtained by a number of highly stereoselective syntheses, a lot of them making use of the Wittig reaction. Ohloff and Pawlak condensed 4,5-epoxy-( )-2-pentenal 228 with the ylide generated from 229 (butyllithium/ether) to the alkadiene epoxide 230 which was oxidized with periodic acid to the 2,4-decadienal 231. 231 is subsequently converted with MnOj/NaCN in ethanol to the pear ester 232162) [75 % (Z)-amount of the C-4 double bond] (Scheme 44). 

The oxidative cleavage of epoxides with hydrogen peroxide gives vicinal hydroxy hydroperoxides [178]. With dimethyl sulfoxide in the presence of trifluoromethanesulfonic acid and diisopropylethylamine, epoxides are converted into a-hydroxy ketones [1014], and with periodic acid, dicarbonyl compounds are formed [761] (equations 343 and 344). 

Epoxides can be easily cleaved with periodic acid or after ring opening to the diol. Branched methyl groups which have not been identified by physical... 

The presence of epoxide groups on the main-chain rubber molecule was first inferred from a reduction in the molecular weight of the rubber after treating acid-hydrolysed natural rubber with periodic acid. " The amount of epoxide was later estimated by hydrogen bromide (HBr) titration and found to be in the range of 45 75mmol/kg of rubber, or 0.3-0.5% mol/mol of rubber. " ... 

The epoxide 43 was cleaved with periodic acid. Periodic acid is soluble in water, but water in any of the reaction steps was thought to cause the removal of the THP protecting group due to possibility of an acidic environment However, 43 could be cleaved with the addition of a small volume of periodic acid dissolved in water without any evidence of loss of the THP protecting group. In the improved preparation of 44, a solution H5IO6 (12.9 g, S6.7 mmol) in water (8 mL) was added dropwise to a solution of 43 (14.4 g, 56.7 mmol) in ether (250 mL) and the mixture was stirred at room ten )erature. The reaction was monitored by GC and was 100% conqjlete after 3 hours. At this point the... 

A number of variations on the procedure exist and have been reviewed by Privett [737]. For example, the positions of double bonds in monoenes containing both cis- and fr"ans-isomers, can be determined by conversion to epoxides, of which the configurational isomers are readily separable, and cleavage of these with periodic acid [245]. Similarly, partial oxymercuration of the double bonds followed by mass spectrometric identification of the products has been applied to the analysis of polyunsaturated fatty acids [719],... 

A color reaction with pyridine has been described for the detection of epoxides (10). 1,2-Epoxides can be detected in a manner similar to 1,2-diols, on reacting them with periodic acid, on the basis of the formation of the colorless precipitate of silver iodate (see p. 177). This reaction is also given by a-hydroxy aldehydes, a-hydroxy ketones, and a-hydroxy acids. 

The principal side reaction to epoxide coupling is hydrolysis. Particularly at acid pH values, the epoxide ring can hydrolyze to form adjacent hydroxyls. This diol can be oxidized with periodate to create a terminal aldehyde residue with loss of one molecule of formaldehyde (Chapter 1, Section 4.4). The aldehyde then can be used in reductive amination reactions. The reaction of an epoxide group with an ammonium ion generates a terminal primary amine group that also can be used for further derivatization. 

Similar oxidants are used for epoxidation of esters of unsaturated carboxylic acids. Methyl oleate is oxidized with peroxybenzoic acid [295] or peroxylauric acid [174] to methyl 9,10-epoxystearate acid in respective yields of 67 and 76%. Alkaline 50% hydrogen peroxide in methanolic solution transforms diethyl ethylidenemalonate at pH 8.5-9.0 and at 35-40 C over a period of 1 h into ethyl 2-ethoxycarbonyl-2,3-epoxybutyrate in 82% yield [145], A somewhat exotic oxidizing agent, dimethyldioxirane, converts ethyl tra/u-cinnamate into ethyl 2,3-epoxyhydrocinnamate in 63% isolated yield [210]. 

Starting with geraniol (126), Sharpless asymmetric epoxidation [68] proceeded in 95% yield and with 93% ee (see Scheme 29) [69]. Hydrobromination of the alkene was achieved under standard conditions using NBS in THF and water (5 1) to afford a 64% yield of diastereomeric bromo alcohols (127). Cyclization to the tetrahydropyran diol was accomplished by treating 127 with camphorsulphonic acid in diethyl ether, followed by diol cleavage with sodium periodate to give a mixture of aldehydes 128 and 129. Upon... 

Hydrolysis of an epoxide with sulfuric or hydrochloric acid as catalyst may proceed poorly because of formation of a sulfuric acid ester or a chloride, and use of an acid incapable of forming an ester is indicated. The reagent of choice is aqueous perchloric acid in tetrahydrofurane, but the more eostly periodic acid is also effective. 

Ckavage with ethereal period acid." In the case of water-insoluble compounds, or where a cleavage product is sensitive to aqueous acid, cleavage of a ptc-glycol or an epoxide of the type formulated can be carried out with a solution of periodic acid in ether or tetrahydrofurane. A solution containing about 16 mg./ml. can be prepared by stirring an excess of the powdered peracid with dry ether or THF for... 

As shown in the Table, with 5 mol% of 1,1-dioxotetrahydrothiopyran-4-one as catalyst,10 epoxidation of various olefins (2-mmol scale) in a homogeneous acetonitrile-water solvent system with 1.5 equiv of Oxone at room temperature can be achieved in a short period of time with excellent yields of epoxides (80-97%) isolated by flash column chromatography.2 As the pH of the reaction is maintained at 7-7.5 by sodium bicarbonate, acid- or base-labile epoxides (entries 12-14) can be easily isolated without decomposition. More importantly, the in situ epoxidation of olefins can be performed on a large scale directly with 5 mol% of tetrahydrothiopyran-4-one, which is oxidized immediately by Oxone to 1,1-dioxotetrahydrothiopyran-4-one during the epoxidation reactions. For example, with 5 mol% of tetrahydrothlopyran-4-one, substrates 3,5 (20 mmol each) and 11 (100 mmol) were epoxidized with excellent isolated yields of epoxides (91-96%). 

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