2-FUNCTIONALIZED AND 8-FUNCTIONALIZED 1,4,7,10-TETRAOXASPIRO[5.5]UNDECANES .4. CONFORMATIONAL STUDY BY H-1 AND C-13 NMR-SPECTROSCOPY

H-1 and C-13 NMR spectra of new 1,4,7,10-tetraoxygenated spiroacetals 1, 2, 3 and 4, were analysed by using 1D and 2D methods. This allowed us to give a definite structural characterization of the E,E, Z,E and EZ isomers obtained by a cyclodehydrative reaction carried out on a di hydroxyketone precursor, under thermodynamic control. The introduction of oxygen atoms in the 4 and 10 positions did not modify the structur al features previously observed for 1,7-dioxygenated spiroacetals obta ined from natural and synthetic sources.