Synthesis and Molecular Structure of Belted Spirocyclic Tetrahydrofurans, A New Class of Preorganized Hosts for Cations

Article abstract of DOI:10.1021/jo00040a041

The preparation and binding properties of spirocyclic tetrahydrofurans 7-11 are described.The condensation of cyclopentanone with 5-lithio-2,3-dihydrofuran (12) provided an alcohol which readily rearranged to ketone 14 under acidic conditions. "Capping" of the carbonyl group in 14 so as to generate a second spiro tetrahydrofuran subunit gave rise to 7 and 8.Starting with cyclobutanone, 2-fold ring expansion involving 12 provided the key reactions leading to 22 and 23, which were "capped" as before.Crystal structure data are available for 9, 11, and 22.In addition, the variable-temperature NMR behaviour of 7 and 10 was quantified by means of 2-D measurements.A detailed analysis is presented that shows the gauche effect to be of major importance in dictating the major conformation adopted by these ionophores.The binding properti s of 7 - 11 have been assayed.Considerable variation was found, the efficiency being critically dependent upon the number of oxygen atoms, the relative stereochemistry of the C-O bonds, and the relative ease of conformational readjustment necessary to achieve proper organization around the oxophilic metal ion.