Formal Synthesis of (±)‐Mitsugashiwalactone and (±)‐Isodihydronepetalactone from Norborn‐5‐en‐2‐one Involving Shapiro Reaction

A formal synthesis of (±)‐mitsugashiwalactone ( 1 ) and (±)‐isodihydro nepetalactone ( 2 ) was accomplished. Baeyer‐Villiger lactonization of ketone 9 followed by acidic treatment led to the rearranged lactone 8 , which underwent a series of functional group transformations to give cyclopentanone derivatives 19 and 20 . Shapiro reaction on 21 and 22 in the presence of excess dry ice gave lactones 5 and 6 . Lactones 5 and 6 previously have been converted to mitsugashiwalactone ( 1 ) and isodihydronepetalactone ( 2 ), respectively.