This project, within the Organic Dynamics Program,is by a young investigator, Robert C. Corcoran of the University of Nevada-Reno, who will study methods for increasing the chemical reactivity of certain oxygen containing organic compounds. The resulting information is expected to aid in the design of catalysts to allow more rapid and/or stereoselective reactions at these functional groups. Stereoelectronic effects in the Lewis acid activation of the oxygen in acetals and carbonyls are to be investigated. In the Lewis acid mediated cleavage of acetals the acid may complex with an oxygen lone pair which is antiperiplanar to the adjacent C-O bond, or to one which is gauche; a kinetic preference for activation of the antiperiplanar lone pair should be observable. Two modes of Lewis acid activation of carbonyl oxygens are possible; in the plane of the carbonyl, or perpendicular to that plane. Though in-plane complexation is generally assumed to be the dominant mode of activation, perpendicular complexation may also play a role. The existence of stereoelectronic preferences in the activation of oxygens in these systems will be investigated by examining conformationally rigid systems which incorporate a Lewis base appendage that can cooperate with the oxygen in question in a chelate ring. The chelation-directed complexation will allow the selective positioning of a Lewis acid with respect to the target oxygen. Rate differences between otherwise similar substrates which are differentially activated in a geometric sense will be an indication of steroelectronic preferences. The determination of such stereoelectronic preferences will aid diastereoselectivity in the reactions of acetals and carbonyl compounds.
