Synthesis of Functionalized Bicyclo[3.2.0]heptanes - a Study of the [2+2] Photocycloaddition Reactions of 4-Hydroxycyclopent-2-enone Derivatives

A selection of 4-hydroxycyclopent-2-enone derivatives were prepared in enantiomerically pure form, and their photochemical [2+2] cycloaddition reactions with a variety of alkenes were studied, with a view to providing diversely functionalized bicyclo[3.2.0]heptanes. Intermolecular reactions provided the target structures in reasonable yields as a mixture of exo and endo adducts, in proportions which varied very little as a function of the steric bulk of the reactants or the reaction conditions. The system was suitably adapted for an intramolecular reaction, which provided a single, stereochemically pure product, the convenient precursor of a rigid, concave, trioxygenated skeleton. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)