Synthesis of, and structural assignments to the stereoisomers of bis (2,2')- and tris (2,2',2")-tetrahydrofurans: conformational features and ionic binding capacities of these gateway polycyclic networks

Construction of the polytetrahydrofuranyl building blocks 6-10 from the common bissiloxyacetone precursor 11 is detailed. The approach is concise and, for the bis-(THF) pair, capitalizes on the full retention of configuration observed during the rhodium-promoted decarbonylation of aldehydes 18 and 19. The capability of the title compounds to associate with alkali metal ions in solution and the gas phase has demonstrated a preference for Li+ over Na+ and K+ in all cases, with 6 and 7 exhibiting somewhat higher binding selectivities than 8-10. The relative energy orderings of attainable conformations with the bis-THF and tris-THF series were explored computationally. The various envelope arrangements present in the individual THF units are shown to play a significant role alongside prevailing gauche interactions. The "gauche effect" is shown computationally not to be an accurate predictor of the lowest energy conformer.