Transition Metal-Catalyzed Stereoconvergent Reactions Utilizing Stereoisomeric Mixtures of Vinylcyclopropanes

Abstract

In the present thesis is discussed the development of four transition metal-catalyzed methodologies. The first is aimed at the synthesis of vinylcyclopropanes (VCPs), which are used as substrates in the three subsequent protocols. These employed stereoconvergent reactions enabling the use of VCPs as regio- and diastereomeric mixtures. The synthesis of the VCPs was realized by copper-catalyzed cyclopropanation of 2-substituted-1,3-dienes. Excellent regioselectivity and enantioselectivity are achieved. The high enantiomeric excesses are preserved through a rhodium-catalyzed intermolecular (5+2) cycloaddition of VCPs with alkynes, delivering enantioenriched 7-membered carbocycles in high yield. The next two projects explore the rearrangement of racemic VCP mixtures to dienoate esters. These dienoates are formed in two distinct substitution patterns. A rhodium catalyst is employed for the cleavage of the VCP ring at the most substituted bond. Complementary regioselectivity is obtained with the use of a ruthenium catalyst. Mechanistic proposals are formulated to account for these distinct outcomes.