Epoxides, cleavage, 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. 

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). 

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],... 

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... 

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... 

An alternative, or supplementary, approach is provided by oxidation with lead tetraacetate or, preferably, periodate, and possibly by identification of the products. Caution must, however, be observed in using this method, as Buchanan has shown that the compound previously designated as methyl 3-chloro-3-deoxy-a-D-gulopyranoside consumes periodic acid extremely slowly (seven days) and is, in fact, methyl 4-chloro-4-deoxy-a-D-glucopyranoside. The products of epoxide cleavage are usually completely defined by these procedures, because irans addition can be assumed, although considerable care must be exercised when there is a possibility of epoxide migration. ... 

In a continuation of his studies on asymmetric P-lactam synthesis, Evans [42] utilized a,P-epoxyaldehydes 49a and 49b, prepared in two steps from achiral allylic alcohols via Sharpless asymmetric epoxidation and Swern oxidation, as chiral glyoxal synthons for the ketene-imine cycloaddition. Diastereosel-ection was excellent, ranging from 90 10 to 97 3 with overall yield of 50 up to 84% (for Schiff base formation and cycloaddition) after recrystallization or chromatographic purification of the major diastereomer. The sense of asymmetric induction correlated with that obtained in the analogous glyceraldehyde reaction, as established by periodic acid cleavage to aldehydes 51. 

In work reported elsewhere (31) we have shown that the oxidation of styrene under mild conditions is promoted by many group VIII metal complexes. The product profile depends on the nature of the metal center and often differs from that observed when radical initiators are used (Table IX). Substantial quantities of styrene oxide are found in some cases but not in others (31). The epoxide which is formed, however, seems to arise via the co-oxidation of styrene and formaldehyde which is formed by oxidative cleavage of the double bond. Formaldehyde may be oxidized to performic acid or formylperoxy radicals which are efficient epoxidizing agents. Reactions of styrene with oxygen in the presence of group VIII complexes exhibit induction periods and are severely retarded by radical inhibitors (31). Thus, the initial step in the oxidation of styrene in the presence of the Ir(I),Rh(I), Ru(II), and Os(II) com-... 

Furthermore, pyrazol-3-ones have been oxidized by a variety of oxidizing agents such as ozone in oxygen, hydrogen peroxide solution, 3-chloroperbenzoic acid, aqueous sodium periodate, lead(IV) acetate with boron trifluoride etherate, or atmospheric oxidation. The reactions lead mainly to epoxidation of an alkene or imine functionality and cleavage of the pyrazol-3-one ring. 

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