E. N. Suslova

1,3-Thiasilacyclopentane and 1,3- and 1,4-thiasilacyclohexane derivatives

Abstract The reaction of dimethyl(chloromethyl)alkenylsilanes, ClCH2Me2Si(CH2)n-CHCH2 (n = 0, 1) with alcoholic KSH solution or thiourea followed by hydrolysis in the latter case leads to the corresponding dimethyl(mercaptomethyl)alkenylsilanes which are unstable compounds readily undergoing polymerization or cyclization. Intramolecular ring closure of dimethyl(mercaptomethyl)allylsilane affords 3,3,5-trimethyl-1-thia-3-silacyclopentane or 3,3-dimethyl-1-thia-3-silacyclohexane, depending on the reaction conditions. Photochemical addition of gaseous H2S to the above dimethyl(chloromethyl)alkenylsilanes yields 3,3-dimethyl-1-thia-3-silacyclopentane and 3,3-dimethyl-1-thia-3-silacyclohexane, respectively. H2S adds to dimethyldivinylsilane upon UV-irradiation to give a mixture of isomeric 2,3,3-trimethyl-1-thia-3-silacyclopentane and 4,4-dimethyl-1-thia-4-silacyclohexane. Thiasilacyclopentane and thiasilacyclohexane derivatives are readily converted to the corresponding sulfonium salts by CH3I. In contrast, 3,3-dimethyl-1-thia-3-silacyclobutane undergoes ring opening to form sulphonium dimethyl(iodomethyl)silylmethiodide, [ICH2Me2SiCH2 S + (CH3)2]I−.

The synthesis and some properties of 1-thia-3-silacyclobutanes and 1-thia-3-silacyclopentane

3,3-Dimethyl-1-thia-3-silacyclobutane has been obtained by the reaction of Me2Si(CH2Cl)2 with potassium hydrosulfide in abs. ethanol. Intramolecular hydrosilylation of isomeric vinylthioethyldiethylsilanes, HEt2SiXSCHCH2 (X = CH(CH3) or CH2CH2) proceeds selectivity as α-addition to afford cyclic compounds, Et2SiCH(CH3)SCHCH3 and Et2SiCH2CH2SCHCH3, respectively. This ring closure reaction is catalyzed by (Ph3P)3RhCl. The endocyclic SiC bond of 3,3-dimethyl-1-thia-3-silacyclobutane undergoes cleavage upon treatment with ethanolic KOH leading to Me2(EtO)SiCH2SCH3 and O(SiMe2CH2SCH3)2. The reaction of 3,3-dimethyl-1-thia-3-silacyclobutane with ethanolic HgCl2 involves ring opening and formation of a complex, O[SiMe2CH2S(HgCl2)CH2HgCl]2.

Synthesis and relative stability of five- and six-membered S-functional derivatives of 1,3-thiasilacycloalkanes

Abstract Oxidation, imidation, and S -methylation reactions of five- and six-membered 1,3-thiasilacycloalkanes have been examined under various conditions. The S -functional derivatives of 1,3-thiasilacycloalkanes undergo solvolytic SiC(S) bond cleavage in protic media. The ease of the ring opening depends on the S -functionality and on the ring size.

Effects of methyl substitution in 4-silathiane S-oxides on the stereochemistry and 1 J CH coupling constants: Buttressing effect of axial sulfinyl group as the origin of the reverse Perlin effect

An NMR study of the products of lithiation/methylation of 4,4-dimethyl-4-silathiane S-oxide 1, diastereomers of 2,4,4-trimethyl-4-silathiane S-oxide 2 and 2,4,4,6-tetramethyl-4-silathiane S-oxide 3, as well as 4,4-dimethyl-4-silathiane S,S-dioxide 4 and 2,4,4-trimethyl-4-silathiane S,S-dioxide 5 is reported. The 2-Me group in 2,4,4-trimethyl-4-silathiane S-oxides is always equatorial while the SO group may occupy either the equatorial (major isomer, 2ee) or axial (minor isomer, 2ae) position. 2,4,4,6-Tetramethyl-4-silathiane S-oxide exists in the form of the two isomers, the one with 2-Me, 6-Me and sulfinyl groups all equatorial (3eee), and the other one as an equilibrium mixture of the axial and equatorial sulfoxides with 2-Me axial and 6-Me equatorial (3aae ⇆s 3eae). The normal Perlin effect (J CHax < J CHeq) is found for the CH2 groups in all studied compounds except for the 3- and 5-CH2 groups in 2ae and 5, which show a small reverse Perlin effect (J CHax > J CHeq). The experimental findings are interpreted in terms of the σ (C‒Hax) → σ* (S˭O) stereoelectronic effect for the C‒H bonds in the 2- and 6-positions, and the buttressing effect of the axial SO group on the C‒Hax bonds in the 3- and 5-positions and confirmed by GIAO-B3LYP/6-311G(d,p) theoretical calculations.

The sila-Pummerer rearrangement of 3,3-dimethyl-3-silathiane S-oxide

Abstract The thermal conversion of sulfoxide 1 into the O-silylated cyclic O,S-acetal ( 2 ) is the first example of the sila-Pummerer rearrangement of cyclic organosilicon sulfoxides leading to ring expansion. The kinetics of the rearrangement are studied and thermodynamic parameters are determined. The results are in compliance with mechanism involving a pentacoordinated silicon atom.

6-Exo and 7-endo photocyclization of αβ-unsaturated organosilicon ω-thiols

Abstract The regioselectivity of cyclization of 3,3- and 4,4-dimethylsila-1-hexene-6-thiols upon UV-irradiation is reported. Ring closure involving the vinyl group at silicon results in the preferred formation of the exo-cyclic product, whereas a high and reversed regio- selectivity is observed when the cyclization reaction occurs via the allyl group at silicon.

Lithiation-methylation of thiasilinane 1-oxides

Lithiation-methylation of 3,3-dimethyl-1λ4,3-thiasilinane 1-oxide and 4,4-dimethyl-1λ4,4-thiasilinane 1-oxide under the action of butyllithium or lithium diisopropylamide and methyl iodide was studied. In both cases, monomethylation proceeds selectively α to the sulfoxide group to form 2,3,3-trimethyl-1λ4,3-thiasilinane 1-oxide and 2,4,4-trimethyl-1λ4,4-thiasilinane 1-oxide, respectively. Subsequently, 2,3,3-trimethyl-1λ4,3-thiasilinane 1-oxide undergoes monomethylation into the same α position to give 2,2,3,3-tetramethyl-1λ4,3-thiasilinane 1-oxide, while 4,4-dimethyl-1λ4,4-thiasilinane 1-oxide is dimethylated into the neighboring α’ position to form two stereoisomers of 2,4,4,6-tetramethyl-1λ4,4-thiasilinane 1-oxide with axial-equatorial or equatorial-equatorial methyl groups in the 2 and 6 positions.

Si-disubstituted diallylsilanes in homolytic thiylation and electrophilic fragmentation reactions

Approaches to Si-disubstituted 1-thia-5-silacyclooctanes based on homolytic addition of hydrogen sulfide to diallylsilanes R2Si(CH2CH=CH2)2 and on intramolecular cyclization of Si-disubstituted (allyl)(γ-sulfanylpropyl)silanes have been studied. In the former case the reactivity of the silanes decreases in the order R = MeO > F > Me > Ph, whereas in the latter case the reactivity order is slightly different: Me > MeO ≈ F ≫ Ph. The reactions of diphenyl-and dimethyldiallylsilanes with the complex BF3·2AcOH occur in a different manner: The former involves rearrangement to form fluoro(2-methylpent-4-enyl)diphenylsilane, while the latter, elimination of the two allyl groups to fluorodimethylsilane and propene.

(N-trifluoromethanesulfonyl)sulfimides of linear and cyclic organosilicon sulfides

The reaction of sodium salt of N-(chloro)trifluoromethanesulfonamide with linear and cyclic fiveand six-membered organosilicon sulfides was studied and their first N-trifluoromethanesulfonyl-substituted imides were synthesized. The results are compared with the data on the reaction of the same substrates with chloramine B. The distinctly pronounced stabilizing effect of a highly electronegative trifluoromethanesulfonyl group was observed, which decreased the reactivity of N-trifyl-substituted sulfimides with respect to electrophilic reagents and increased their stability. Mass spectra of isomeric cyclic organosilicon N-trifluoromethanesulfonyl-substituted sulfimides VII, X, their acyclic analog III, and the product of the decomposition of the latter at the Si-C(S) bond IV were studied. The mechanism of formation of sulfimides in nonaqueous media is discussed.

Comparative reactivity of substituted 1,3-and 1,4-thiasilinane S-oxides in the sila-Pummerer rearrangement and inversion of the thiocarbonyl group

The thermal sila-Pummerer rearrangement of diastereomeric 2,3,3-trimethyl-1,3-thiasilinane S-oxides was studied. Introduction of the methyl group in the 2 position of 3,3-trimethyl-3-thiasilinane S-oxide slows down the rearrangement. When heated in CCl4, the trans isomer (2-Meeq, SOeq) converts into the cis isomer (2-Meeq, SOax) which rapidly rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. On the contrary, the isomeric 2,4,4-trimethyl-1,4-thiasilinane S-oxide is thermally stable up to 160°C in DMSO. The inversion at the sulfur atom in 2,3,3-trimethyl-1,3-thiasilinane S-oxides and 2,4,4-trimethyl-1,4-thiasilinane S-oxides under the action of triethyloxonium tetrafluoroborate was studied. The trans isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Meeq, SOeq) forms with Et3O+BF4− a salt which decomposes in two ways. The first involves recovery of the starting sulfoxide due to Sn2 substitution at the carbon atom of the ethoxy group, and the second, convertion into the cis isomer (2-Meeq, SOax) which rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. Under the same conditions, the cis isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Meeq, SOeq) decomposes to form siloxanes. trans-2,4,4-Trimethyl-4-thiasilinane S-oxide (2-Meeq, SOeq) under the action of Et3O+BF4− convers into the cis isomer (2-Meeq, SOax). The B3LYP/6-311G(d,p) theoretical analysis showed that the thermal inversion at the sulfur atom in the compounds studied has a high energy barrier.