Studies toward the total synthesis of garsubellin a:: A concise synthesis of the 18-epi-tricyclic core

During studies directed toward the total synthesis of garsubellin A, a concise stereocontrolled synthesis of the 18-epi-tricyclic compound 3 was achieved. Key steps were a one-pot stereoselective construction of the bicyclic lactone 23 followed by a formal migration to the bicyclo-[3.3.1]nonane-1,3,5-trione and an intramolecular Wacker-type tetrahydrofuran ring formation.