Sulfoxides, allylic labeling

In contrast to benzyl p-tolyl sulfoxide 37, allyl p-tolyl sulfoxide 217 racemizes between 50 and 70°C. The values of the activation energy and the entropy (A/f = 23 kcal/mol AS = -4.9 e.u.) as well as the absence of decomposition products are indicative of a different racemization mechanism for this sulfoxide. In this connection, it is interesting to note that the condensation of p-toluenesulfenyl chloride with allyl alcohol labeled in the a-position with deuterium... 

The oxidation of benzylic alcohols was quantitative within hours and selective to the corresponding benzaldehydes, but the oxidation of allylic alcohols was less selective. The oxidation of aliphatic alcohols was slower but selective. In mechanistic studies considering oxidation of benzylic alcohols, similar to the oxidation of alkylarenes, a polyoxometalate-sulfoxide complex appears to be the active oxidant. Further isotope-labeling experiments, kinetic isotope effects, and especially Hammett plots showed that oxidation occurs by oxygen transfer from the activated sulfoxide and elimination of water from the alcohol. However, the exact nature of the reaction pathway is dependent on the identity of substituents on the phenyl ring. 

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