A 1H nuclear magnetic resonance study of alkyl- and aryl-substituted 1,4-oxathian-2-ones

Abstract

¹ H N.m.r spectra for a number of alkyl- or aryl-substituted 1,4-oxathian-2-ones were analysed using the LAOCOON III program. The coupling constants imply that the C-S-C-C portion of the ring has a normal cyclohexane-like conformation which is compatible with either a classical boat or a half-chair. Chemical shift, geminal coupling constant, and long-range coupling constant evidence is presented which suggests that the former conformation is prevalent for oxathianones. Compounds with a single alkyl or phenyl substituent at C-3 or C-6 are conformationally biased, whereas the substituents at C-5 are mobile with ΔG° 1.0 and 1.7 kJ mol^–1 for 5-methyl and 5-phenyl, respectively.