Studies on the Total Synthesis of Hainanolide (Ⅵ)-The First Access to the Lactone Functionality

C2a-β-H ketone 6 was synthesized from the exo-IMDA-additive 4 with the aid of singlet oxygen, and ring E of hainanolide was assembled via kinetic enol ether of 6.     

Studies on the Total Synthesis of Hainanolide (VI)-The First Access to the Lactone Functionality

The intramolecular Diels-Alder reaction (IMDA) stands as the t'undamental strategy inour total synthesis of hainanolide l, to assemble the tricyclic skeleton. ring B. C and D.as it was reported 1. Cyclization of triene 2 afforded a mixture of endt,-IMDA-additive3 and exo-IMDA-additive 4, the ratio of which varied with reaction conditions. Yetneither 3, with the C2. hydrogen at a position, nor 4, with the C, methyl at a position.fits the configuration of that in the natural product. The…