Chemoselective control elements

In Heading 1.4 we have already seen that three different kinds of control elements [3] may be considered 1) chemoselective control elements (controlling chemical reactivity), 2) regioselective control elements (controlling the orientation of reactants) and 3) stereoselective control elements (controlling the spatial arrangement of atoms within the molecule), which may control either the relative (diastereoselective) or the absolute spatial arrangement (enantioselective control elements). 

Chemoselective control elements protecting and activating groups. Latent functional groups... 

Sometimes, instead of using protecting groups as chemoselective control elements it may be more convenient to resort to activating groups as, for instance, the S-2-pyridylcarboxylic esters (24) which react intramolecularly to give macrolides 25 in excellent yields [20] (Scheme 12.7). 

Coupling reactions between allyltins and allyl chlorides are assumed to proceed via bis(7T-allyl)palladium intermediates Yamamoto [9] has shown that in the presence of aldehydes or imines, it is possible to control the chemoselectivity of the reaction so that either the allyl halide or the aldehyde/imine is allylated by the organotin. The key element is coordination of a ligand, such as triphenylphosphine, which is suggested to form a trigonal palladium complex with an and an /jCallyl... 

---