SYNTHESES, X-RAY STRUCTURES AND CONFORMATIONAL STUDIES OF TETRAOXA[N.N]METACYCLOPHANES

New types of macrocyclic ligands with tetraoxa[n.n]metacyclophane mole cular skeletons have been synthesized. The structures of 4,28-dibromo- 1,8,15,22-tetraoxa[8.8]metacyclophane 2a, 2-dibromo-1,10,17,26-tetraox a[10.10]metacyclophane 2b, 4,28-dibromo-2,7,16,21-tetraoxa[8.8]metacyc lophane 3a, 32-dibromo-2,9,18,25-tetraoxa[10.10]metacyclophane 3c, 6-d ibromo-2,11,20,29-tetraoxa[12.12]metacyclophane 3d, 0-dibromo-2,13,22, 33-tetraoxa[14.14]metacyclophane 3e and 14,28-diiodo-2,7,16,21-tetraox a[8.8]metacyclophane 9a have been determined by single-crystal X-ray s tructure analyses. In compounds 2a and 2b, two bromide atoms face each other within the macrocyclic ring while in compounds 3c, 3d and 3e th e bromine atoms face in opposite directions, outwards from the macrocy clic ring. In the smaller ring compounds 3a and 9a the structure was i ntermediate between these two types. Substitution of the bromine atoms via lithiation has been achieved smoothly with iodine and methyl iodi de as the electrophiles to afford disubstituted compounds in good yiel ds, while with trimethylsilyl chloride as the electrophile the mono-su bstituted compound has been obtained.