Novel Route to Functionalized Cyclooctanoids via [5+3] Cycloaddition

The self-dimerization of 3-oxidopyrylium leading to stereocontrolled formation of highly functionalized cyclooctanoids is described. Different functionalities were introduced on the dimer (3) and the stereochemical outcome was determined by single-crystal X-ray analysis. It is noteworthy that the hydrogenation of 3 in ethanol solvent gave the transannulated product 5, whereas the expected dihydro product 4 was obtained when the reaction was run in nonnucleophilic solvents. The mechanistic pathway is discussed.