An asymmetric total synthesis of (+)-pentalenene

A stereoselective total synthesis of (+)-pentalenene was achieved through the tandem cycloaddition reaction of the allenyl diazo substrate prepared from (+)-citronellal. The initial intramolecular [2+3] cycloaddition reaction between the diazo functionality and the allenyl group produced the trimethylenemethane (TMM) intermediate after immediate loss of nitrogen molecule from the cycloaddition intermediate. Subsequent [2+3] cycloaddition of the TMM with olefin produced the angularly fused triquinane structure stereoselectively.