Conformational analysis of the thiolane ring system. I. Stereochemistry of the base-catalyzed hydrogen-deuterium exchange, pyramidal inversion, and proton magnetic resonance spectrum of trans-3-methyl-3-thioniabicyclo[4.3.0]nonane iodide, a conformationally rigid thiolanium cation

Abstract

The pmr spectrum of the title compound (II) can be analyzed by a first-order procedure. The compound undergoes stereospecific base-catalyzed exchange of the a ring protons, whose reactivities are found to be approximately in the ratio 200:3:3:1. Nuclear Overhauser experiments on specifically deuterated samples indicate the faster proton to be cis to the 5-methyl group. This stereochemical assignment together with the values of the vicinal coupling constants disclose the stereochemistry of the heterocyclic part of II. Certain consequences of this stereochemistry are discussed. The stereospecificity of the H-D exchange is discussed in relation to its significance in terms of the stereochemistry, retention or inversion, of the exchange, as well as in relation to the Wolfe and Czimadia theory on the conformational energy of species having adjacent lone pairs. Finally, the availability of a specifically deuterated sample has permitted the observation of the occurrence of thermal pyramidal inversion of the sulfur atom, and the measurement of the rate of this process.

Stereochemistry of .alpha.-halogenation of sulfoxides. 1. A proton nuclear magnetic resonance study of the bromination of trans-2-thiahydrindan 2-oxide

“…The S-methyl derivative of thiahydrindan-I,/,3,3-d4 (3) was prepared as previously described. 24 From previous work this sulfonium salt was known to undergo highly stereoselective base-catalyzed H/D exchange at position R2. 24 Treatment of 3 with 2N NaOH in H20 (7 h, 60 °C) resulted in 80% exchange at the R2 position giving D. This was subjected to thermal pyramidal inversion at sulfur, a process which exchanges corresponding positions across the sulfur atom.24 Indeed the material (E) obtained through thermal equilibration of D had the H label equally divided between the quasi-equatorial « positions.…”

“…24 From previous work this sulfonium salt was known to undergo highly stereoselective base-catalyzed H/D exchange at position R2. 24 Treatment of 3 with 2N NaOH in H20 (7 h, 60 °C) resulted in 80% exchange at the R2 position giving D. This was subjected to thermal pyramidal inversion at sulfur, a process which exchanges corresponding positions across the sulfur atom.24 Indeed the material (E) obtained through thermal equilibration of D had the H label equally divided between the quasi-equatorial « positions. This material was once more subjected to H/D exchange to obtain F. This was ion exchanged to obtain the chloride salt which was subsequently pyrolyzed to eliminate gaseous CH3CI, leaving behind the labeled sulfide G. This material was oxidized to the sulfoxide H, whose NMR spectrum in the presence of shift reagent is reported in Figure 4.…”

“…The NMR of the undeuterated sulfonium salt in D20 has been previously described. 24 The recovered material, D, had 80% protium content at 3.40 corresponding to H2.…”

Ionic liquids based on S-alkylthiolanium cations and TFSI anion as potential electrolytes

“…Some cyclic sulfonium salts, such as S-methylthiolanium iodides [26,27] , had been reported, but these were not concerned with electrochemical properties or applications. In this work, several ILs based on S-alkylthiolanium cations and TFSI − anion as shown in Table 1 were synthesized and characterized; the relation between the structure and the melting point and the viscosity is discussed.…”

Towards a complete account of the mechanism of hydrogen isotope exchange of diastereotopic protons of carbon acids. II. Acid- and base-catalyzed enolization of bicyclo[2.2.1]heptan-2-ones. Evidence for exchange by inversion

“…While our analysisX is based on hydrogen isotope exchange a to a carbonyl group, it must also hold for exchange of diastereotopic protons for all carbon acids such as sulfoxides (32)(33)(34)(35), sulfones (35), sulfonium salts (36), and N-nitrosoamines (37)" where a common intermediate is generated or the barrier to inversion of the incipient diastereomeric anions is less than the barrier to protonation. Although the barriers to inversion of carbanions appear to be quite low (38), we expect that in the case where diastereomeric anions are formed and the inversion barrier is high, provided the primary, secondary, and SIEs are not vastly different for the fast and slow protons, (kr/ks)H'D = (kr/kJD' H. Presently, we are studying H + D and D + H exchange in several sulfoxides and plan to report our findings in the near future.…”