Studies towards the total synthesis of Zoanthamine: Synthesis of the ABC ring system via a [4+2] cycloaddition

ORGN 188

Martin Juhl, juhl@kemi.dtu.dk, Department of Chemistry, Technical University of Denmark, Kemitorvet 1, building 201, Kgs. Lyngby, 2800, Denmark
In an ongoing endeavor to carry out our projected total synthesis of the marine alkaloid zoanthamine, an elaborate model study was conducted starting from ()-carvone. In 9 steps alkenyl iodides corresponding to the C11-C24 fragment of 1 was obtained. The alkenyl iodides were coupled to various stannanes (C6-C10) through the Corey modification of the Stille reaction, affording a variety of Diels-Alder precursors (1). An interesting and highly unexpected cascade reaction sequence was observed during the screening of the intramolecular Diels-Alder reaction, generating a novel tetracyclic framework (2). A slight modification in the Diels-Alder precursor allowed the desired Diels-Alder reaction to take place in 62-87% yields.