ABIOLOGICAL CATALYSIS FOR SYNTHETIC EFFICIENCY

Synthetic efficiency requires reactions that are both selective and economical in terms of atom count. The invention of new transition metal catalyzed reactions provides a powerful approach to both problems. Palladium complexes have been particularly fruitful in creating new reactions. By use of such complexes to resolve a chemoselectivity problem, cyclizations to medium sized rings becomes efficient. An approach for controlling regioselectivity in palladium catalyzed allylic alkylations invokes tethering two reactants either by hydrogen bonding or covalently. The metal complex may become a template to impose diastereoselectivity that violates the thermodynamic preferences of the product. A new type of chiral environment to promote enantioselectivity now allows asymmetric C-C bond formation in excess of 95% ee. These methods evolve efficient syntheses of glycosidase inhibitors allosamidine and mannostatin A. While many of these methods are atom economical, this goal requires exploration of other processes. Transition metal catalyzed reactions of acetylenes are particularly fruitful territory for exploration. Palladium catalyzed isomerization of acetylenes to allenes and insertion into acetylenic C-H bonds provide two new processes, both of which when applied intramolecularly effect cycloisomerization to macrocycles. Palladium complexes are not unique in their synthetic utility. A ruthenium catalyzed condensation of allyl alcohols and terminal acetylenes constitutes an effective synthesis of beta,gamma-unsaturated ketones which is a simple addition of the two reactants with reorganization of the oxidation pattern.