Abstract

Cyclic 8-, 9-, 10-, and 12-membered bis(anisylphosphonothioyl)disulfanes were synthesized. Next, structurally related 7 to 9-membered cis and trans sulfanes were isolated as a result of sulfur atom extrusion from the parent cyclic disulfanes. The results of the desulfurization of the disulfanes were compared to the results obtained for desulfurization of the respective bis(anisylphosphodithioates). Cyclic disulfanes predominantly provide trans-sulfanes, and the expansion of their ring sizes causes the cis/trans isomer ratio of the cyclic sulfanes to increase. Moreover, bis(anisylphosphodithioates) mainly afford cis-sulfanes, and the cis/trans isomer ratio is greater than 3 : 1. Mechanistic and stereochemical aspects of cyclic disulfane desulfurization have been presented. Although cis-sulfanes are more stable than their respective trans isomers, the cyclisation is a kinetically controlled reaction, which results in predominance of trans-sulfanes in the case of trans-disulfane desulfurization. Disulfanes exhibit thermal and solvolytic stability. A characteristic persistent deep-blue coloration of methanolic ammonia solutions is an unusual feature of cyclic disulfanes. The mechanism of their ammonolysis has been studied and has been compared to that of the respective reaction performed on acyclic disulfanes. Ammonia solution of an acyclic disulfane is colourless. Detailed X-ray analysis was performed for all trans-disulfanes and cis- and trans-sulfanes. They were compared to each other and to their acyclic or cyclic known analogs that comprise common subunits. 8-, 9-, 10-, and 12-membered disulfanes exist as trans isomers exclusively both in the solid state and in solution. They are more stable than their hypothetical cis isomers. The PSSP torsion angles of cyclic disulfanes lie in the range of 94 - 125o and increase with the size of the ring. The greater stability of the cis-sulfanes can be ascribed to the characteristic anisyl–anisyl stacking. Weak hydrogen bonds (CH. . .O/S) play a role in conformational stabilization and intermolecular interactions. The conformations of cyclic disulfanes and cyclic sulfanes were also preserved in solution. A Karplus relationship has been established between the dihedral angles and vicinal H–P coupling constants for all disulfanes and sulfanes. The effects of solvent on the 1H NMR chemical shifts (ASIS) were associated with the dipole moments of the sulfanes.

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