Two similar dibenzo cyclic ethers with dissimilar conformations

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Burns, Dennis H.
Meece, Frederick A.
Moore, Curtis E.
Eichhorn, David M.
Acta crystallographica. Section C, Crystal structure communications. 2009 Jan; 65(Pt 1): o27-30.
Two dibenzo cyclic ether compounds, 6,12-dibromodibenzo[d,i]-1,2,3,6,7,8-hexahydro-1,3-dioxecin (systematic name: 8,16-dibromo-2,4-dioxatricyclo[,10)]octadeca-5,7,9,14,16,18-hexaene), C(16)H(14)Br(2)O(2), (II), and 8,14-dibromodibenzo[f,k]-1,5-dioxa-1,2,3,4,5,8,9,10-octahydrocyclododecene (systematic name: 7,19-dibromo-11,15-dioxatricyclo[,10)]icosa-5,7,9,16,18,20-hexaene), C(18)H(18)Br(2)O(2), (III), were prepared as scaffolding for phosphate-anion receptors. In both compounds, the two aromatic rings are linked by three methylene units ortho to the oxygen substituent of each ring. The only difference between the two compounds is the number of methylene units linking the two ether O atoms. The dibenzo cyclic ether with an ether linkage of one methylene unit adopts a chair-like conformation, where the two aromatic rings are parallel to each other. On the other hand, the dibenzo cyclic ether with an oxygen linkage of three methylene units adopts a bowl-like conformation. The latter scaffold configuration is the only structure of the two that would allow for the placement of convergent functional groups necessary for the establishment of an anion-selective binding pocket.
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