Support-Bound Sequestering and Scavenging Agents

The use of PSRs as described in the earher sections of this chapter has been restricted to one-step transformations. However, a highly interesting application of PSRs was first described by CainelH and colleagues [118] in 1980, and further developed by Parlow [120] and more especially by Ley et al. [121-124]. These groups described the use of several PSRs within one reaction sequence. Reactive species such as oxidants and reducing agents do not react with each other when they are polymer-supported consequently, one-pot transformations that cannot be realized in conventional solution-phase chemistry are possible. 

Another process was described by Parlow [120], in which sec-phenethyl alcohol 

These were further sulfonylated using polymer-supported sulfonylpyridinium ion 156 to give sulfonamides 157 [121], 

Various other sequential, clean, multistep transformations based solely on PSRs have been described. Starting from alcohols 152, which were oxidized to the corresponding carbonyl compounds (153), a,fi-unsaturated ketones 158 were prepared by a Mukaiyama aldol condensation using Nafion-TMS 159 as silylating agent and 

Lewis acid [122], The resulting enones 158 were treated with hydrazines 160 to give clean final products, 4,5-dihydro-lH-pyrazoles 161 [122]. 

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