Solid-phase-supported reagents and scavengers

All of the reactions discussed up to this point are conducted in such a manner that the growing molecule of interest is bound to a solid support. Another important method 

Solid-supported reagents which have found utility include Nafion-scandium Lewis acid catalyst (allyl additions to aldehydes) [62], HOBt (medium-ring lactamization) [63], EDC (preparation of active esters) [64], and thiazolium hydrotribromide (brominations) [65], A review has also appeared describing the use of supported reagents in separation science, primarily for the selective sequestration of metal ions [66], 

As recent as three years ago, the synthetic chemist had a limited portfolio of reactions which could be conducted on solid phase and most of the useful reactions involved carbon-heteroatom bond formation, in particular, carbon-nitrogen bonds. An explosion in interest in combinatorial chemistry techniques has brought solid-phase synthesis back into the spotlight. During the past 18 months, a number of groups have published on the solid-phase synthesis of complex, functionality-rich small molecules. At the current rate of progress, one would expect that, within a few years, the synthetic chemist will have the ability to tackle nearly any synthesis using solid-phase techniques. 

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An evaluation of a potential solid support begins by first determining which method or methods will be used to monitor what is attached on the particular support. Certain types of supports are not compatible with all of the available methods of analysis or, at least, not as easy to evaluate as others. Table 1 lists the major techniques available to monitor solid-phase reactions. Measuring the absorbance of a UV-active group cleaved off a support and elemental analysis of the support itself are both methods 

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