Allylic alcohols rearrangement during oxidation

Hydroxyl groups are stable to peracids, but oxidation of an allylic alcohol during an attempted epoxidation reaction has been reported." The di-hydroxyacetone side chain is usually protected during the peracid reaction, either by acetylation or by formation of a bismethylenedioxy derivative. To obtain high yields of epoxides it is essential to avoid high reaction temperatures and a strongly acidic medium. The products of epoxidation of enol acetates are especially sensitive to heat or acid and can easily rearrange to keto acetates. 

From these results it seems that the epoxy alcohol, IX, does not arise via an intramolecular vanadium-catalyzed rearrangement of cyclohexenyl hydroperoxide, V. An alternative pathway is an intermolecular epoxida-tion reaction between the allylic hydroperoxide, V, and the allylic alcohol which is formed during the oxidation (Reaction 17). We found that IX was produced from reaction of V with VII in the presence of [C5H5V-... 

Last (but not least) propylene oxide undergoes rearrangement in the presence of base and forms allyl alcohol, thus forming in situ initiators during the alkoxylation process. Unless properly accounted for, this decreases the molecular weight of the polyether produced. 

In the first approach shown in Scheme 9, ketoester 77 was alkylated successively with 4-bromobutene and 1,3-dibromopropene. After decarboxylation, 78 was converted into iV-aziridinylimine 79 in good yield. The pivotal radical cyclization reaction proceeded smoothly to produce a mixture of isomeric propellane compounds 80, which was purified after the epoxidation step. For the synthesis of modhephene, the mixture of epoxides was rearranged into the corresponding allylic alcohols 81 and then the allylic alcohols were oxidized, giving a separable mixture of unsaturated ketones 82a and 82b. The major product 82a possessed the correct stereochemistry of the methyl group of modhephene. Since 82a had already been converted into modhephene, a formal total synthesis of dZ-modhephene has thus been completed. The isomeric ratio of 80 reflects the stereoselectivity during the radical cyclization reaction. The selectivity was very close to the ratio reported by Sha in his radical cyclization reaction. ... 

An oxidative rearrangement took place during the MCPBA epoxidation of the secondary allylic alcohol auraptenol, leading to the enal shown in equation (20). This reaction has been used in an approach to casegravol and in a synthesis of amottinin. The reason why the intermediate epoxy alcohol undergoes rearrangement in this case is not known beyond the possibility that the m-chlorobenzoic acid by-product could act as an acidic catalyst. 

A carbonyl transposition can be effected via the addition of a vinyl or an alkyl Grignard reagent to an a, 3-unsaturated ketone. Acid-catalyzed rearrangement of the resultant allylic alcohol during oxidation with PCC affords the transposed a,(3-unsaturated carbonyl substrate. This reaction represents a useful alternative when Wittig olefination of the ketone is problematic. 

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