Peroxyacids, reaction with effects

In the absence of the activating second carbonyl functionality, it is necessary to use more ingenious methods to produce the same net effect. These procedures more often than not involve radical reactions. Among them is the thermolysis of tert-butyl esters of peroxyacids 437, which are readily synthesized in a standard esterification of tert-butyl hydroperoxide with an acid chloride. Decarboxylation proceeds via an initial homolytic cleavage of the 0-0 bond, elimination of CO2, and reduction of the incipient alkyl radical by an added hydrogen atom donor such as 438 (Scheme 2.143). Examples showing the exceptional synthetic importance of this decarboxylation procedure will be presented later. 

Neighboring group effects are important in reactions of peroxyacids, as they were with reactions of hydroperoxides. Reexamination of the epoxidation of 171 using MCPBA rather than TBHP reveals that the peroxyacid gave a 95 5 mixture of 172 and 173. Using MCPBA rather than TBHP led to a slight increase in diastereoselectivity for the reaction, although this depends on the substitution pattern of the alkene. Sharpless... 

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