Acyloxylation intramolecular

In contrast to intramolecular cyclizations, the intermolecular addition of O-centered radicals to ti systems as initiating step in complex radical cyclization cascades has only recently attracted considerable attention. The reason for the low number of papers published on O radical addition to alkenes and alkynes could originate from the perception that O-centered radicals, such as alkoxyl radicals, RO, or acyloxyl radicals, RC(0)0", may not react with 7t systems through addition at rates that are competitive to other pathways, for example, allylic hydrogen abstraction and p-fragmentation in the case of RO" or decarboxylation in the case of RC(0)0" (Scheme 2.9). 

Electrolysis of the dicarboxylic acid (LVII) in an MeOH-MeONa-(Pt) system and subsequent workup afford the keto acid (LVIII), a precursor of chrysanthemic acid (LVffl), in 86% yield via intramolecular acyloxylation and acid-promoted hydrolysis [139] ... 

A number of intramolecular acyloxylations have been reported [135-143], two examples of which are given in Eqs. (43) and (44). 

RXN47 Intramolecular Amination, Alkoxylation or Acyloxylation of Alkynes... 

Other ways to generate unsaturated acyloxyl radicals have been used. For instance, Moriarty studied the lead tetraacetate oxidation of e carboxylic acid and, after an extensive mechanistic study, he concluded that the y-lactone observed was formed by electrophilic attack on the double bond. " The same explanation can probably be applied to other examples of lactone formation resulting from lead tetraacetate oxidation of ethylenic acids. The formation of a y-lactone has also been reported by anodic oxidation of endo-norbomene-5-carboxylate, possibly by intramolecular addition of the acyloxyl radical but oxidation of the double bond, as proposed for the anodic oxidation of e do-norbornenemethanol, could not be completely discarded. ... 

It appears then that the only unambiguous case of an intramolecular addition of an acyloxyl radical has been described by Sustmann, who used a strained system (71) in which ff-scission of the acyloxyl radical to give a cyclopropyl radical was probably less favored than in other cases (Scheme 38). The yield of Cy5 (72) is 2% and that of Cy6 products (73) 31% [22% (X = H), 5% (X = r-BuO) and 4% (X = PhCHMe)]. It must be noted that a very low Cy5/Cy6 ratio is observed, but that because of the special character of the system studied, it does not seem reasonable to ascribe this result to unexpected behavior by the acyloxyl radical. 

In conclusion, except for this one case, there is, until now, no clear evidence for the intramolecular addition of acyloxyl radical. But this may be due to difficulty in generating unsaturated acyloxyl radicals rather than being a characteristic of these radicals. 

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