CONFORMATIONAL-ANALYSIS OF THIA CROWN-ETHER DERIVATIVES BY NMR-SPECTROSCOPY AND MOLECULAR MECHANICS CALCULATIONS

Addition of sulfur dichloride to tetrachlorocatechol-bisallylether (1) yields the 9- and 10-ring thia crown ether derivatives 2 and 3, respe ctively, together with the dithia-18-crown-6-ether 4. The 10-membered ring compound 3 represents the first thia macrocycle containing both M arkovnikov and anti-Markovnikov constitution of the beta-chloro-thio s tructural segments in the same molecule. By H-1 and C-13 NMR spectrosc opy, equal amounts of two preferred conformers of the only isolated di astereomer of 3 were observed at temperatures below -50 degrees C. The signals were assigned to these conformers using COSY, HETCOR, and pha se sensitive NOESY spectra at low temperatures. The preferred conforma tions and the relative configuration were determined using the differe nt effects of gamma(gauche)- and gamma(anti)-positions in C-13 NMR che mical shifts and analyzing vicinal (3)J(H,H) coupling constants. These results were confirmed by molecular mechanics calculations.