Synthesis with Donor-Acceptor-Substituted Vinylcyclopropanes

Abstract

The concept of using 2-alkenylsubstituted 2-siloxycyclopropanecarboxylates as protected enones is introduced. Efficient synthesis of these compounds as well as simple ring cleavage variants are described. In-situ reaction of the liberated enones with hetero nucleophiles or carbon nucleophiles allows preparation of a variety of functionalized γ-oxocarboxylate derivatives. Of special interest are adducts obtained from nitro alkanes in high yields. These are precursors for natural products as the pheromone chalcogran or the macrolides pyrenophorin and vermiculine, respectively. Intramolecular 1,3-dipolar cycloaddition of a nitrone - gained from one of these nitro alkane adducts - as well as intramolecular Diels-Alderreactions provide stereoselective entries to polycyclic systems. Implications of these strategies for natural product synthesis are discussed. An alternative approach to donor-acceptor-substituted vinylcyclopropanes by use of Fischer carbene complexes is also represented. Thus, vinyl-substituted Cr(0) carbene complexes transfer this ligand cleanly to electron-deficient alkenes to afford vinylcyclopropanes. The second route to these compounds involves methyl dienoates and their highly stereoselective reaction with simple Cr(0) carbene complexes.