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Synthetic approaches to 4,4-dimethyl-1,4-thiasilinane and its S-functional derivatives, 4,4-dimethyl-1,4-thiasilinane S-oxide, 4,4-dimethyl-1,4-thiasilinane S,S-dioxide, 4,4-dimethyl-1-(phenylsulfonylimino)-1,4-thiasilinane, and 1,4,4-trimethyl-1,4-thiasilinan-1-ylium iodide, were studied. The S-functional derivatives of 4,4-dimethyl-4-thiasilinane, unlike 3,3-dimethyl-3-thiasilinane, are hydrolytically stable.Thiasilinanes form an interesting class of heteroatomic cyclohexane derivatives. Thiasilinanes differ from earlier studied diheterocyclohexanes (dioxanes, dithianes, and oxathianes) in that they contain two heteroatoms of different nature: sulfur with a lone electron pair and silicon that exerts a strong inductive effect and, at the same time, has vacant d orbitals.Thiasilinanes have poorly been studied [136], while their S-functional derivatives have been unknown. In the course of the research into the properties and transformations of silathiacycloalkanes we have synthesized 3,3-dimethyl-1,3-thiasilinane S-oxide [7], 2,3,3-trimethyl-1,3-thiasilinane S-oxide, 2,3,3-tri-ÄÄÄÄÄÄÄÄÄÄÄÄ methyl-1,3-thiasilinane S,S-dioxide [8], 3,3-dimethyl-1-(phenylsulfonylimino)-1,3-thiasilinane, and 1,3,3-trimethyl-1,3-thiasilinan-1-ylium iodide [9, 10], and studied their transformations [10]. These works have primarily focused on 1,3-thiasilinanes; the only available information on 1,4-thiasilinanes related to the synthesis of 1,4-thiasilinane and its sulfonium salt, 1,4,4-trimethyl-1,4-thiasilinan-1-ylium iodide [4]. Proceeding with this research, in the present work we developed new synthetic approaches to 4,4-dimethyl-4-thiasilinane (I), synthesized their S-oxides II3V, and studied their hydrolytic stability.

4,4‐Dimethyl‐1‐(trifluoromethylsulfonyl)‐1,4‐azasilinane 1 and 2,2,6,6‐tetramethyl‐4‐(trifluoromethylsulfonyl)‐1,4,2,6‐oxazadisilinane 2 were studied by variable temperature dynamic 1H, 13C, 19F NMR spectroscopy and theoretical calculations at the DFT (density functional theory) and MP2 (Møller‐Plesset 2) levels of theory. Both kinetic (barriers to ring inversion) and thermodynamic data (frozen conformational equilibria) could be obtained for the two compounds. The computations revealed two minima on the potential energy surface for molecules 1 and 2 corresponding to the rotamers with the CF3SO2 group directed ‘inward’ and ‘outward’ the ring, the latter being 0.2–0.4 kcal/mol (for 1) and 1.1 kcal/mol (for 2) more stable than the former. The vibrational calculations at the DFT and MP2 levels of theory give the values of the free energy difference ΔGo for the ‘inward’ ‘outward’ equilibrium consistent with those determined from the experimentally measured ratio of the rotamers. The structure of crystalline compound 2 was ascertained by X‐ray diffraction analysis. Copyright © 2011 John Wiley & Sons, Ltd.

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The crystal and molecular structures of trans-2,4,4-trimethyl-4-silathiane 1-oxide 1 and 4,4-dimethyl-4-silathiane 1,1-dioxide 2 were determined by single crystal X-ray diffraction. Both compounds have the chair conformation with the 2-Me and the S=O group in compound 1 occupying the equatorial positions. The DFT (B3LYP/6-311G(d,p)) and MP2 (MP2/6-311G(d,p)) theoretical calculations nicely reproduce the X-ray experimental geometry. The obtained results are discussed in connection with the electronic and structural properties of the compounds.