CYCLOPHANES .35. DNMR, MOLECULAR MECHANICS, AND CRYSTAL-STRUCTURES OF 2,11-DITHIA[3.3]ORTHOMETACYCLOPHANE AND 2,11-DITHIA[3.3]ORTHOPARACYCLOPHANE

The syntheses of 2,11-dithia[3.3]orthometacyclophane (5) and 2,11-dithia[3.3]orthoparacyclophane (6) by dithiol-dibromide coupling are described. Whereas the yield of 5 is not significantly affected by the substrate pairing, that of 6 is. Both compounds exhibit a temperature-dependent H-1-NMR spectrum. An energy barrier of 11.0 +/- 0.2 kcal/mol (45.7 +/- 0.8 kJ/mol) has been calculated for 5, but that of 6 was too low to be determined. Slightly contrasting results were obtained from two different molecular mechanics programs for the relative energies of the six limiting conformations of 5. Crystal structure determinations of 5 and 6 have been carried out, and the conformational behavior of 5 and 6 in solution and in the solid state is discussed.