Chemistry of the SO bond. Part 11. trans,trans-4,6-Di-t-butyl-trans-5-methyl-1,3,2-dioxathiane 2-oxide and cis,cis-4,6-di-t-butyl-cis-5-methyl-1,3,2-dioxathiane 2-oxide, synthesis and crystal structure determination

Reduction by LiAlH4 of 2,2,4,6,6-pentamethylheptane-3,5-dione gives a mixture of diastereoisomeric diols, which upon cyclisation with thionyl chloride yields a mixture of isomeric 4,6-di-t-butyl-5-methyl-1,3,2-dioxathiane 2-oxide. From the distribution of the latter mixture, a small, but distinct stereoselectivity of the dione reduction is inferred, which in turn suggests a preference of the reacting dione for an extended conformation.Single crystal X-ray determinations have been performed on the two title compounds (components of the cyclic sulphite mixture) to establish their structure, conformation and geometry. The geometries are compared with currently available population averages of cyclic sulphites. The high substitution present in the title compounds does not show in the C–O–S(O)–O–C region of the ring, but reveals itself markedly in the C(4)–C(6) region and in the substituents.