Acetoxy group radicals

In some instances, the resist polymer can be prepared in a single step by direct polymerization of the protected monomer(s) (37,88), entirely avoiding the intermediate PHOST. HOST-containing resist polymers have also been prepared by free-radical copolymerization of a latent HOST and a stable, acid-labile monomer, eg, the copolymerization of acetoxystyrene with tert-huty acrylate, followed by selective removal of the acetoxy group (89) (Fig. 30). 

This step is unlikely. There is no relief of steric strain as the acetoxy group is still present and the C-H bond strength is higher than the 0=C0-C bond strength by about seven kcal/mole (26). In addition the acyloxy radical is unstable and decomposes exothermically (26). If this happens during dismutation, loss of acetoxy is favored even more, up to thirty kcal/mole. 

In contrast to anionic 1,4-addition methods, the radical procedure tolerates an acetoxy group adjacent to the reactive center (radical - bearing carbon). In applying this general method to tetraacetylglucosyl bromide 7, products 9, with an axial C-C bond, and 10 are obtained in a ratio of ca. 10 1. ESR experiments show that the radical intermediate has the boat conformation 8. The attack that leads to the axial product 9 is, therefore, the favored... 

The reaction with carbon tetrahalides [213] probably involves free-radical attack e.g. by CBra) rather than electrophilic attack on the enol, but is still subject to selection of the reaction site leading to the more stable conjugated product (c/. p. 159). The reaction with methyl chloride (and a base) has been described only in a patent [214], and no mechanistic details are available. It is surprising that so unreactive an electrophile should attack the enol ether. There is no clear reason for chloromethylation favouring C(4), beyond the suggestion [21 ] that the reagent may first form a complex with the 3-acetoxy group. 

If organosilicon compounds have an acetoxy group on the carbon adjacent to the silicon atom, a facile 1,2-shift of the acetoxy group from carbon to silicon has been observed1 s, in addition to capture of the initially formed silyl radical by abstraction of halogen from the CC14 solvent (equation 3). Similar behavior was shown by a related benzyldimethylsilyl... 

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