A convergent synthesis of the trans-fused hexahydrooxonine ring system andreproduction of conformational behavior shown by ring F of ciguatoxin

A new strategy for the construction of the fused hexahydrooxonine ring syst em has been developed. The present synthesis involves an intramolecular rea ction of gamma-allcoxyallylsilane with acetal to form an O-linked oxacycle and a SmI2-mediated intramolecular Reformatsky reaction for constructing an oxonane ring as the key steps. Thermodynamic behavior of the trans-fused h exahydrooxonine ring was clarified for the first time and the conformationa l alternation was reproduced in the 6-9-6 tricyclic model compound 1 as was observed for that in the ciguatoxin molecule (ring F). (C) 1999 Elsevier S cience Ltd. All rights reserved.