Synthesis and Multinuclear NMR Characterizations of Some (3.3)Diselena‐ and (4.4)Tetraselenacyclophanes.

Abstract Several symmetrical and unsymmetrical bis-selenacyclophanes were prepared and characterized by multinuclear ( 1 H, 13 C{ 1 H} and 77 Se{ 1 H}) NMR. The symmetrical cyclophanes of phenyl, furyl, pyridyl and thiophenyl appear to exist in predominantly syn conformation in solution at room temperature. VT- 1 H NMR of some cyclophanes indicate that the equilibrium between the syn conformers which differ in the disposition of the bridge seleniums (symmetric about mirror planeahsymmetric about inversion center) can be slowed at low temperatures. Interesting 13 C{ 1 H} shifts are observed in unsymmetrical cyclophanes containing 2,2'-biphenyl, pyridine and furan. The 77 Se{ 1 H} chemical shifts appear to be related to the size of the cavity of the cyclophanes.