Non-planar aromatic compounds. Part 4: Fine tuning the degree of bend in the pyrene moiety of [7](2,7)pyrenophanes by modifying the nature of the bridge

Structures for several mono-, di-, tri- and tetraoxa[7](2,7)pyrenophanes were calculated at the AM1 level of theory and the bend angle (theta) of the pyrene system was found to be affected by both the number and the position(s) of the oxygen atom(s). In varying the type of atom X at the theta position, B was predicted to decrease with the C-X bond length. Attempted synthesis of 1,4,7-trioxa[7](2,7)pyrenophane gave traces of the target compound as the minor component of a mixture with its recovered precursor. H-1 NMR evidence supports the prediction that it possesses a more bent pyrene unit than that of the current record holder. 4-Oxa[7](2,7)pyrenophane was prepared readily in 11% overall yield over ten steps and its crystallographically measured bend angle is 102.9 degrees. (C) 2001 Elsevier Science Ltd. All rights reserved.