Asymetric hydroboration is a powerful method for the construction of structurally diverse organic compounds in optically active form. We are investigating the design and synthesis of monomeric chiral boranes and their use in asymmetric hydroboration. We have prepared a prototypical monomeric reagent which is now readily available in quantity and in very high chemical and optical purity. This internally-coordinated alkyl chloroborane ether complex is a valuable reagent for asymmetric hydroboration of simple alkenes. Herein we propose several important extensions of our current work. We will seek to develop a simple, general procedure for obtaining optically pure materials by purification of the diastereomeric intermedies generated in our hydroboration reactions. In two cases studied thus far we have obtained optically pure alcohols in good overall yield. The (+) enantiomer of our chloroborane reagent will be pepared. To this end we will devise a synthesis of (+)-nopol from the abundant (+) enantiomer of Alpha-pinene. The B-deuterio analog of the chloroborane will be synthesized using the previously unknown reagent C1BD2-SMe2. Stereospecifically deuterated, optically active alcohols and carbonyl compounds will thereby become readily available. Asymmetric hydroborations of allylic alcohol derivatives will be systematically investigated. These studies should furnish valuable insights concerning electronic effects on the efficiency of asymmetric induction, and will also provide a group of particularly valuable structures as products. We have found that our reagent can be employed in asymmetric cyclic hydroborations of dienes. Hydroborations of this type have not been reported previously and will be extensively investigated. Modified reagents will be prepared in order to probe the mechanism of the hydroborations, which cannot be elucidated from kinetic studies. Molecular mechanics calcuations will also be employed to evaluate possible pathways. To explore the utility of asymmetric hydroboration in functionalized, complex systems with preexisting chirality, we propose a synthesis of the erythronolide A seco acid. In our approach, asymmetric hydroborations are used to generate eight of the eleven sterogenic carbon atoms.
