Oxygen‐18 labeling of cyclic and acyclic sulfinate esters

Abstract

Both cyclic and acyclic sulfinate esters were labeled with at the sulfinyl oxygen by acid-catalyzed isotope exchange with H i 8 0 or alkaline hydrolysis in H2"0 followed b:y re-esterification. Long-range isotope effects on the l3C NMR chemical shifts were observed.Isotopically labeled substrates are useful in investigations of reaction mechanisms as well as structure elucidations. The oxygen of sulfinic acid derivatives is a key atom of the functional group of this class of compounds, and L80-labeled sulfinate esters were previously prepared from labeled sulfinic acids or sulfinyl chlorides [l]. All these procedures are not efficient either in terms of isotopic or chemical yield. We now present in this article simple procedures for obtaining I80-labeled sulfinate esters of both cyclic and acyclic structures by isotope exchange. These procedures are based on the mechanisms of reactions of the esters.A sulfinate ester undergoes acid-catalyzed transesterification in an alcoholic solution (Equation l) [2] and hydrolysis in an acidic aqueous solution equilibrium with sulfinic acid in an acidic aqueous alcoholic solution and that the isotope would be incorporated in the ester as well as in the acid if we used I80-enriched water as a cosolvent (Equation 2). This was successfully achieved with methyl benzenesulfinate. ni RS(0)OR' + H2I80 RS(0) "OH Hi + R'OH RS(180)0R' -H 2 0 (2)It was found that a cyclic sulfinate ester (sultine) undergoes ring opening in an aqueous alkaline solution, while the corresponding hydroxy sulfinic acid cyclizes in acid [4]. The cyclic sulfinate is stable in an acidic aqueous solution. An equilibrium of the intramolecular hydrolysis-esterification shown in Equation 3 is largely on the side of the ester, even in aqueous solution. Although the apparent reaction cannot be seen, the sultine must be in a dynamic equilibrium (Equation 3) in aqueous acid. Therefore, the isotope should be incorporated into the sultine in a solution containing I80-enriched water.? RESULTS AND DISCUSSION Preparation of Benz-Fused SultinesSulfinate esters used in this article are summarized in Scheme 1. Acyclic sulfinate esters are prepared by nucleophilic substitution of sulfinyl derivatives by alcohols, while cyclic sulfinates 0 1993 VCH Publishers, Inc.

Evidence for Hypervalent Intermediate in Aminolysis Reaction of Ethylbenzene Sulfinate

“…If the 18 O isotope exchange or a break of pH rate profile are observed during the reactions, these could be taken as good piece of evidence for sulfurane intermediate. These observations were successful in the hydrolysis of sulfinate ester 6 and sulfinamides. 7 However, it is still to be clarified whether the simple nucleophlic substitution reactions at sulfur atom take place through a sulfurane.…”

Synthetic methodologies in organic chemistry involving incorporation of [17O] and [18O] isotopes

“…Both cyclic and acyclic sulfinate esters were labeled by Okuyama et al . at the sulfinyl oxygen by acid‐catalyzed isotope exchange or alkaline hydrolysis in H 2 18 O.…”

On the mechanism of hydrolysis of sulfinate esters: oxygen isotope exchange and theoretical studies

“…45 atom %. 8 The side products were the sulfinic acid and a small amount of S-phenyl benzenethiosulfonate, eqn. (3).…”