Syntheses, X-ray structures and conformational studies of tetraoxa[n.n]metacyclophanes

Abstract

New types of macrocyclic ligands with tetraoxa[n.n]metacyclophane molecular skeletons have been synthesized. The structures of 14,28-dibromo-1,8,15,22-tetraoxa[8.8]metacyclophane 2a, 16,32-dibromo-1,10,17,26-tetraoxa[10.10]metacyclophane 2b, 14,28-dibromo-2,7,16,21-tetraoxa[8.8]metacyclophane 3a, 16,32-dibromo-2,9,18,25-tetraoxa[10.10]metacyclophane 3c, 18,36-dibromo-2,11,20,29-tetraoxa[12.12]metacyclophane 3d, 20,40-dibromo-2,13,22,33-tetraoxa[14.14]metacyclophane 3e and 14,28-diiodo- 2,7,16,21-tetraoxa[8.8]metacyclophane 9a have been determined by single-crystal X-ray structure analyses. In compounds 2a and 2b, two bromide atoms face each other within the macrocyclic ring while in compounds 3c, 3d and 3e the bromine atoms face in opposite directions, outwards from the macrocyclic ring. In the smaller ring compounds 3a and 9a the structure was intermediate between these two types.

Substitution of the bromine atoms via lithiation has been achieved smoothly with iodine and methyl iodide as the electrophiles to afford disubstituted compounds in good yields, while with trimethylsilyl chloride as the electrophile the mono-substituted compound has been obtained.