SIMPLE DESIGNS FOR THE CONSTRUCTION OF COMPLEX TRANS-FUSED POLYETHER TOXIN FRAMEWORKS - A CONVERGENT STRATEGY BASED ON HYDROXY KETONE CYCLIZATION OF C-LINKED OXACYCLES

A single, unified convergent strategy for the stereocontrolled synthes is of trans-fused polyethers was developed. It was demonstrated that t he epimerization and reductive intramolecular coupling of hydroxy keto nes in reactions with silane-Lewis acids (SI-LA) to generate ethers in C-linked oxacycles is affected by its conformational preference in a predictable manner. The obtained results make evident that the influen ce of hydrogen bonding between a hemiketal hydroxyl and a 1,3-diaxial C-O bond is regular and predictable and that convergent synthesis of t rans-fused polyethers may confidently be conducted on driving ring clo sure to oxane rings under thermodynamic conditions.