Conformational analysis of thia crown ether derivatives by NMR spectroscopy and molecular mechanics calculations

Abstract

Addition of sulfur dichloride to tetrachlorocatechol-bisallylether (1) yields the 9- and 10-ring thia crown ether derivatives2 and3, respectively, together with the dithia-18-crown-6-ether4. The 10-membered ring compound3 represents the first thia macrocycle containing bothMarkovnikov andanti-Markovnikov constitution of the β-chloro-thio structural segments in the same molecule. By1H and13C NMR spectroscopy, equal amounts of two preferred conformers of the only isolated diastereomer of3 were observed at temperatures below −50°C. The signals were assigned to these conformers using COSY, HETCOR, and phase sensitive NOESY spectra at low temperatures. The preferred conformations and the relative configuration were determined using the different effects of γ gauche -and γ anti -positions in13C NMR chemical shifts and analyzing vicinal3 J H,H coupling constants. These results were confirmed by molecular mechanics calculations.