Formal Asymmetric Synthesis of Pentalenolactone E and Pentalenolactone F-1. Retrosynthesis and π-Facial Differentiation in Palladium-Catalyzed and Dipolar [3 + 2]-Cycloaddition Reactions of Bicyclic Alkenes: Evidence for Electrostatic Control of Stereoselectivity
in which the hydroxy group occupies the pseudoaxial position, to be the more stable one. According to force-field calculations, the 5E-conformation seems to be stabilized by an intramolecular electrostatic interaction between the hydroxylic oxygen atom and the lactonecarbonylgroup, corresponding to the initial step of an intermolecular nucleophilic attack at the carbonylgroup. The O−C1 distance and