Organic synthesis using chemical tags: The "third leg" of parallel synthesis

Increasing emphasis has recently been placed on the development of syntheti c methods which effectively couple chemical synthesis and purification. For example, new formats for parallel synthesis are being developed which invo lve attachment of chemical tags to both reagents, reactants, and substrates to permit their chemoselective removal from reaction mixtures. The driving force for the development of tagged organic reagents is the ability to use standard solution-phase chemistry methods and reaction monitoring techniqu es (e.g. TLC and HPLC). In this mini-review, we will outline recent develop ments on the growing class of chemically tagged reagents, reactants, and su bstrates and highlight examples of their use in multistep synthesis.