Acid chlorides peroxyacids

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. 

The retrosynthesis of an ester TM typically begins with a disconnection at either C-O bond. Formation of this bond always involves a nucleophilic oxygen reacting with an electrophilic carbon that is either acyl (a carboxylic acid derivative such as acid chloride) or alkyl (RX), causing a substitution to take place. If the alkoxy group is highly substituted (or is a phenoxy derivative), the Sn2 approach is unsuitable so the TM must be prepared by acyl substitution or by peroxyacid oxidation of the corresponding ketone. 

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