The focus of this research will be on intramolecular 3+2 and 4+3 cycloaddition recations of allyl cations with dienes. Alkoxyallylic alcohols, cyclopropane hemiacetals and allylic sulfoxides will be used as progenitors of allylic cations. A detailed study of regioselectivity and relative stereochemistry will be made in the context of the synthesis of fused 6,7 and 6,5 bicyclic ring systems. %%% With this Renewal award, the Synthetic Organic Program is supporting the research of Professor Michael Harmata of the Department of Chem,istry at the University of Missouri, Columbia. Dr. Harmata will focus his work on developing a class of reactions known as cycloadditions for the purpose of constructing compounds containing 5,6 and 7-membered rings, structures often occuring in important natural products.