13. The internal cyclopropanation of exocyclic acrylates and the subsequent vinylcyclopropane-cyclopentene rearrangement were used in an efficient synthesis of a key intermediate, triquinane 23, containing all of the contiguous quaternary centers. The utilization of abnormal Reformatsky reaction of 4-bromocrotonates with keto esters served in the preparation of important precursors to the cyclopentene annulation sequence, the ...