Structural characterization of new dispiranes and postulated molecular structure of their propellane isomers

Tetratosylate of 1,1,2,2-tetrakis(hydroxymethyl)cyclopentane was employed as a substrate in a reaction scheme leading to constitutionally symmetrical seven-membered dispiranes with oxygen and sulfur heteroatoms. In both cases, an alternative product, the eight-membered propellane isomer, was not obtained. Conformation analysis based on X-ray structure determination and energy optimization revealed that oxygen dispirane possesses an exact twofold symmetry and twist-boat conformation of the heteroring, as predicted from energy minimization. In contrast, its sulfur counterpart has different conformations for both heterorings (chair vs. twist-boat), different from the calculated one. q 2003 Elsevier B.V. All rights reserved.