8. Synthesis, X-ray and conformational studies of novel tetrazole-containing macrocycles: 4,13-dioxa-1,7,8,9,17,18,19,20-octaazatricyclo[14.2.1.17,10]icosa-8,10(20),16(19),17-tetraene and 4,14-dioxa-1,7,8,9,10,18,19,20-octaazatricyclo[15.2.1.07,10]icosa-8,10,17(20),18-tetraene Vadim Yu. Zubarev,Rostislav E. Trifonov,Vyacheslav V. Filichev,Vladimir A. Ostrovskii,Andrew D. Abell,Michael K. Edmonds J. Chem. Soc. Perkin Trans. 2 2001 417