Stereochemistry of 1,3-dithia-5,6-benzocycloheptene-s-oxides

According to dynamic 13C NMR spectroscopy trans-2-R-(R ¼ Ph, Me, Et, Pri)-5,6-benzocycloheptene-1-oxides at 260 8C in CDCl3 exist as an equilibrium mixture of the chair and boat forms with the substituents in the equatorial position. Unsubstituted (R ¼ H) compound has in addition a boat form with an axial sulfinyl group, whereas for But derivative conformational equilibrium is anancomerically shifted to the boat structure. X-ray study of trans-2-isopropyl-1,3-dithia-5,6-benzocycloheptene-1,3-dioxide displays a chair form with equatorial alkyl substituent and axial-equatorial SO-moieties. q 2003 Elsevier B.V. All rights reserved