Abstract
The crystal structures of endo, endo-2,5-dibromo-9-oxabicyclo[4.2.1]nonane, (I), C8H12Br2O, endo, endo-2,5-bis(phenylthio)-9-oxabicyclo[4.2.1]nonane, (II), C20H22OS2, and 9,10-dioxatricyclo[4.2.1.12,5]decane, (III), C8H12O2, were determined and the conformations of these transannular O-heterocyclization products of cycloocta-1,5-diene were defined. The structure determinations reveal a tetrahydrofuran ring having an envelope conformation and an oxepane ring with a twisted chair-conformation in each of (I) and (II), with the two bulky substituents quasi-equatorial or quasi-axial, respectively, both in a trans-position in relation to the ring O atom. The tricyclic compound (III) consists of two five-membered envelopes and a 1,4-dioxane chair. The cylooctane moiety has a twisted chair-conformation in both (I) and (II), whereas it is a chair in (III).
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