9321454 Welker The focus of this research is the use of transition-metal substituted 1,3-diene complexes as substrates in cycloaddition reactions, especially in Diels-Alder reactions. Transition-metal substitution will be utilized to enhance the reactivity of dienes as well as enhance the regio- and stereoselectivity of subsequent cycloaddition reactions of these dienes, especially in control of exo-endo ratios of Diels-Alder products. It will be demonstrated how simple changes in the metal's coordination sphere can profoundly alter the stereochemical outcome of subsequent Diels-Alder reactions thus providing some practical solutions to long standing reactivity problems associated with the use of Z- and 1,1-disubstituted dienes in this reaction. Cleavage reactions involving the metal substituted cycloadducts will show how these metal substituted dienes can serve as synthons for several dienes which normally have low reactivity in Diels-Alder reactions. Transition-metal substituted chiral dienes will be investigated as useful reagents for asymmetric Diels-Alder reactions involving acyclic dienes which are invariably poorer substrates in catalytic asymmetric Diels-Alder reactions than cyclic dienes. %%% With this award the Synthetic Organic Program is supporting the research of Dr. Mark E. Welker of the Department of Chemistry at Wake Forest University. Professor Welker will focus his work in the area of development of synthetic methodology using transition-metal substituted diene complexes in cycloaddition reactions, one of the most important methods for constructing complex ring systems. ***
