Hydroxy acids from aryl iodides

R is usually aryl or vinylic.1627 The formation of a-keto acids1628 or esters1629 requires more severe conditions. a-Hydroxy acids were obtained from aryl iodides when the reaction was carried out in the presence of an alcohol, which functioned as a reducing agent.1630 Cobalt catalysts have also been used and require lower CO pressures.1625 OS V, 20, 739. 

Linkers that enable the preparation of y-lactones by cleavage of hydroxy esters from insoluble supports are discussed in Section 3.5.2. Resin-bound y-lactones have been prepared by Baeyer-Villiger oxidation of cyclobutanones [39], by intramolecular addition of alkyl radicals to oximes [48], by electrophilic addition of resin-bound sele-nenyl cyanide or bromide to 3,y-unsaturated acids (Figure 9.2 [100]), and by palladium-mediated coupling of resin-bound aryl iodides with allenyl carboxylic acids (Entry 10, Table 5.7 [101]). 

Starting from a vinyl-substimted resin, hydroboration with 9-BBN yields a homobenzylb-orane (Scheme 9). This intermediate can be coupled with various functionalized aryl iodides as well as vinyl and alkyl iodides giving rise to resins with amide, ester, or protected hydroxy functionaUties.t Similarly, bromostyrene could be coupled with functionalized boranes for the attachment of preformed handles, for example, for the construction of the silicon traceless linker.t i The carbometaUation of certain alkenes such as tropanes and the subsequent treatment with aryl boronic acid gives rise to two new C—C bonds (Scheme 10). 

As found by Engman et al. (1999), sodium alkyltelluroates are excellent reagents for the generation of aryl radicals from the corresponding iodides in the dark. Accordingly, l-(2-iodo-phenyl)-l-methyloxirane reacts with two equivalents of sodium 1-butyltelluroate giving 2,3-dihydro-3-hydroxy-3-methylbenzo[( ]tellurophene, which was isolated in 62% yield. The latter was readily converted into 2,3-dihydro-3-methylbenzo[( ]tellurophene on treatment with a catalytic amount of p-toluenesulfonic acid (94% yield Scheme 7.42). 

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