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Thiane-l-oxide

Stereoselective conversion of a thiane 57 to the corresponding tmns-thiane-l-oxide 58 was achieved by bromonium ion mediated electrooxidation while a preferential formation of the cis-sulphoxide 58 was observed under acidic electrolysis123 (equation 38). [Pg.253]

The basicity of the sulfoxide oxygen has been investigated by observing infrared shifts in protic solvents. ° In this way, it was shown that thietane 1-oxide is more basic than cyclobutanone, but less basic than tetramethylene sulfoxide (thiolane 1-oxide) or pentamethylene sulfoxide (thiane l-oxide). ° Toward phenol, the order of basicity is as follows thiolane 1 -oxide > diethyl sulfoxide > thiepan 1-oxide > dimethyl sulfoxide > thiane 1-oxide > 9-thiabicyclo[3.3.1]nonane 9-oxide > 7-thiabicyclo[2.2.1]heptane 7-oxide > thietane 1-oxide.ThepKaof the conjugate acid of thietane 1-oxide is — 1.92, as determined in aqueous sulfuric acid. =... [Pg.480]

Isomerization of cyclic sulfoxides. Johnson and McCams found that dinitrogen tetroxide equilibrates 4-substituted thiane-l-oxides. Treatment of either the cis-isomer (1) or the trans-isomer (2) gives an equilibrium mixture of the composition o... [Pg.167]

While the value suggested by Johnson and McCants for the conformational free energy difference in Scheme 3.2 was a substantial AG°9q.c = +1.3 kcalmol [13], a more precise determination was carried out by Lambert and Keske [14], who examined the slow-exchange nuclear magnetic resonance (NMR) spectra of the unsubstituted tetradeuteriated thiane-l-oxide (2) at -90°C (Scheme 3.3). [Pg.65]

More recently, Abraham and coworkers [18] reexamined the conformational behaviour of thiane-l-oxide (3) by analysis of lanthanide-induced shifts (LIS) in the appropriate NMR spectra. Their results compare reasonably well with those obtained by Barbarella et al. [17], suggesting the applicability of the LIS method to sulfoxide conformational analysis. [Pg.66]

The molecular structure of thiane-l-oxide has been determined by gas-phase electron diffraction [19]. The collected data indicate that the molecule adopts a chair conformation with an axial orientation of the oxygen atom, and there was no indication of any appreciable amount of equatorial form [20]. [Pg.66]

By contrast, substitution of an axial hydrogen with a methyl group, as in 3,3-dimethylthiane-l-oxide (5), gives rise to an equilibrium in which only the equatorial conformer was observed at low temperature in CD2CI2 [22-24] (Scheme 3.5). Apparently, the steric repulsion between the diaxial substituents in (5-ax) overwhelms the effect responsible for the axial preference in thiane-l-oxide, whatever its nature. [Pg.67]

Interestingly, force-field calculations have been carried out on sulfoxides (3) and (5) [16,25]. The preference of thiane-l-oxide for the axial conformation was found to be due to a repulsion of the equatorial oxygen atom by its vicinal hydrogen atoms - not to an attraction of the axial oxygen atom by its syn-axial hydrogen atoms. The equatorial preference in 3,3-dimethylthiane-l-oxide is caused by van der Waals repulsion from the syn-axial methyl group. [Pg.67]

In a related study, the conformational equilibrium of 4-oxo-thiane-l-oxide (8) (Scheme 3.16) was determined by Anteunis and colleagues [35] as —90% axial and 10% equatorial. The free energy difference (AG298K = +1.3kcalmol ) is definitively larger than in thiane-1-oxide itself. [Pg.71]

More recently, Nagao and colleagues [40] described the conformational analysis of cis- and rrans-4-benzyloxy- and 4-siloxy-substituted thiane-1-oxides (cis-(12) and trans- 12)) at -80°C in CD2CI2. The results are collected in Table 3.2, and show that in the cases of c/s-4-RO-thiane-l-oxide (Scheme 3.23A), their RO-ax conformer preferences are 45% (12a), 66% (12b), and 67% (12c), respectively. In the cases of trans-4-RO-thiane-l-oxide (Scheme 3.23B), the preferences of RO for the axial position are higher. [Pg.74]

Table 3.2 Conformer ratio in RO-substituted cis- and fran -thiane-l-oxide (12) ... Table 3.2 Conformer ratio in RO-substituted cis- and fran -thiane-l-oxide (12) ...
Substitution of an a-methylene group in thiane-l-oxide by oxygen ((3) - (15)) results in a greater predominance of the axial conformer [47] (Scheme 3.27). In fact, Harpp and Gleason interpreted the 100-MHz H NMR spectrum of 1,2-oxathiane-2-oxide (15) in terms of a single axial conformation. [Pg.76]

That the substitution of an a-methylene group by sulfur in thiane-l-oxide (3) to give the cyclic thiosulfinate (23) results in a greater predominance of the axial conformer (Scheme 3.37) was first proposed by Harpp and Gleason in 1971 [47] and was confirmed by several groups in the early 1980s [62-64]. [Pg.80]

Nevertheless, it has been demonstrated by Lambert et al. [22] that the introduction of a gem-dimethyl group at C-3 in thiane-l-oxide to afford (5) strongly disfavours the axial conformer (see Section 3.2.2). For example, comparison of the conformational equilibria in 1,3-oxathiane 5-oxide (17) and 5,5-dimethyl-l,3-oxathiane 5-oxide (18) suggests that the magnitude of the syn-diaxial CH3/S=0 interaction amounts to 1.3kcalmol [55] (see Section 3.3.2). [Pg.80]

Hydrogen-bonding forces were also found to be quite important in the conformational behavior of fran. -2-(a-hydroxybenzyl)thiane-l-oxide E. L. Eliel, E. M. Olefirowicz, M. T. Alvarez, D. J. Hodgson and D. K Towle, Heterocycles, 28, 937 (1989). [Pg.93]

The preference for the axial position in unhindered thiane-1-oxides has been known for some time. The spectra of the cis and trans isomers of the 2-, 3- and 4-methyl thiane-1-oxides, 169-171, were also measured. It was concluded from the 13C chemical shifts that the methyl groups preferred the equatorial positions. A comparison of the 170 chemical shifts obtained for sulfoxides 169-174 with those obtained for the cis and tram sulfoxide isomers of trans- 1-thiadecalin, 175 and 176, was consistent with this proposal. Sulfoxide 175 with the S=0 axial gave a shift about 17 ppm upfield from that of its equatorial isomer 176. For sulfoxides 169-174, the conformers proposed to have the S=0 axial gave shifts that were upfield from those of the supposed equatorial conformers. For tram-3, (rans-5-dimethylthiane-1 -oxide (177) with the oxygen axial, the 170 signal was 21 ppm upfield from the signal observed for the equatorial oxygen in cis-3, cis-5-dimethylthiane-l-oxide (178). [Pg.87]

Thian 4-tert.-Butyl- -1-imid-l-oxid Ell, 1303 (R2SO + HN3) Thiocarbamidsaure N-Butyl-N-ethyl- -S-ethylester E4,... [Pg.680]

Thian -l-(4-methyl-benzolsulfo-nylimid)-l-oxid Ell, 1307 (R2SO + R-S02-N3)... [Pg.1045]

Much of the sustained interest in the conformational analysis of sulfoxides was initiated by the discovery of the axial preference of the sulfinyl oxygen in thiane-1-oxide. Indeed, although Henbest and Khan [12] reported that the thermally-induced equilibrium of 4-/-butylthiane-l-oxides (1) afforded a cis.trans ratio of 20 80, a reexamination by Johnson and McCants established that the isomer bearing the axial oxygen is more stable [13] (Scheme 3.2). [Pg.65]

Thiolans, Thians, Thiepans, Thiocans, and their Oxides and Dioxides Synthesis.—The intramolecular trapping of a sulphenic acid by a carbon-carbon double bond constitutes a new stereospecific route to cw-2-substituted thiolans and thian 1-oxides. Thus 5-t-butylsulphinylpent-l-ene (1), when heated at... [Pg.217]

In this synthesis the geometry of the acyclic double bonds is controlled through their formation as part of the thiane ring. Thiacyclohexanone (711) was converted to 4-thia-l-methylcyclohexene by reaction with methylmagnesium iodide and subsequent dehydration. Metallation of (712) with s-butyllithium and alkylation of the anion with the epoxide (713) gave a tertiary alcohol which was dehydrated to yield (714). A second alkylation of (714) with trails-4-chloro-3-methyl-2-butene 1-oxide (715) completed the carbon skeleton of the Cis juvenile hormone. Reduction of (716) with lithium in ethylamine and then desulfurization with Raney nickel led to trienol (717), a product converted previously to (718). [Pg.480]

On the basis of these and related results, and because variation of the oxidant did not produce the clear-cut differences in the steric course of oxidation observed with thianes, it was suggested66 that control of the S-oxidation of derivatives of 2-hydroxy-l,4-oxathiane is best achieved by changing the configuration at the anomeric center an axially attached substituent such as methoxyl or acetoxyl engenders equatorial S-oxygenation, whereas an equatorially attached, anomeric substituent leads to an axial S-oxide. [Pg.224]

The same procedure was performed with nerol oxide to give the crystalline lactone in 22% yield257. With 2-(l-propenyl)thiane the thiolactone only was obtained in 8% yield. The naturally occurring 10-membered lactones ( )-phoracantholides 1 and J were prepared using this methodology257. [Pg.44]

A range of 2-substituted 1,3-dithiins has been synthesised from 2-zincio-l,3-dithianes and di(thian-2-yl)zinc <97SYN1174>. 1,3-Dithiane 1-oxides have been obtained by enantioselective oxidation using micro-organisms <97T9695>. [Pg.310]


See other pages where Thiane-l-oxide is mentioned: [Pg.544]    [Pg.79]    [Pg.544]    [Pg.79]    [Pg.962]    [Pg.962]    [Pg.231]    [Pg.179]    [Pg.67]    [Pg.151]    [Pg.153]    [Pg.159]    [Pg.858]    [Pg.411]    [Pg.234]    [Pg.467]    [Pg.467]    [Pg.340]    [Pg.243]    [Pg.301]    [Pg.1080]    [Pg.221]    [Pg.69]   
See also in sourсe #XX -- [ Pg.65 ]




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