Entropy-controlled asymmetric synthesis. How differential activation entropy is induced in chiral tethered reactions

[GRAPHICS] Kinetic measurements to determine effective molarities of intramolecular re actions using 2,4-pentanediol and related tethers showed that methyl groups on the tether accelerate the major diastereomeric process but decelerate t he minor process. The efficient promotion of stereocontrol is suggested to be due to chiral perturbation of the reaction rate through the entropy term , The conformation of the encounter complex of the reagent and reactant moi eties was deduced by stereochemical analysis of the intramolecular adducts.