14-20 (a) 1 ) tert-Butyl hydroperoxide is the oxidizing agent. The (CH3hCOOH contains the 0-0 bond just like a peroxyacid. 2) Diethyl tartrate has two asymmetric carbons and is the source of asymmetry; its function is to create a chiral transition state that is of lowest energy, leading to only one en anti orner of product. This process is called chirality transfer. 3) The function of the titanium (IV) isopropoxide is to act as the glue that holds all of the reagents together. The titanium holds an oxygen from each reactant-geraniol, t-BuOOH, and diethyl tartrate-and tethers them so that they react together, rather than just having them in solution and hoping that they will eventually collide. (b) All three reactants are required to make Sharpless epoxidation work, but the key to enantioselective epoxidation is the chiral molecule, diethyl tartrate. When it complexes (or chelates) with titanium, it forms a large structure that is also chiral. As the t-BuOOH and geraniol approach the complex, the steric requirements of the complex allow the approach in one preferred orientation. When the reaction between
This is the end of the preview.
access the rest of the document.