Ring opening and closure and oxygen isotope exchange of cyclic sulfinate esters

Abstract

Alkaline ring opening and the reverse ring closure in an aqueous acid solution of cyclic sulfinate esters (sultines), 3H-2,l-benzoxathiole 1-oxide (la) and 3,4-dihydro-2,l-benzoxathiin 1-oxide (lb), have kinetically been studied at 25 O C . The sultine la is more reactive than l b in both the opening and closure reactions. However, acid-catalyzed oxygen isotope exchange of the 180-labeled sultine la was found to be slower than that of the labeled lb. The contrasting reactivities of the five-and sixmembered sultines in alkaline and acid solutions as well as the reaction mechanisms are considered on the basis of the ab initio molecular orbital calculations. Nucleophilic substitution of sulfinic acid derivatives may proceed stepwise through a trigonal-bipyramidal (hypervalent) intermediate or concertedly in an sN2 manner (eq 1). Most of such reactions occur with predominant ine 0 / \ X Y-s-x / .f\R \ + Y version at the chiral sulfur, and a mechanism involving a hypervalent intermediate has been suggested? though the S~S-like mechanism cannot be excluded. Hydrolysis of a sulfinate ester (eq 2) is formally similar to that of a carboxylate ester. Tetrahedral intermediates for the carboxylate hydrolysis were demonstrated by showing that the oxygen isotope exchange can be observed during the reaction.3 A possible l8O exchange occurring 1 8 0 1 h$~o\Yd\s RS("0)DH + R'DH

Synthesis and Aminolysis of N,N-Diethyl Carbamic Ester of HOBt Derivatives

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Carbamates are characterized by the lone pair of electrons on N, which can delocalize into the π*orbital of the carbonyl group by an ηN → π* C=O interaction (similar to that reported for ηN → π* C=S interaction). 15 This facilitates the formation of a tetrahedral structure, which can be a transition state in the concerted mechanism or an intermediate in the stepwise one.…”

“…22 The aminolysis of heterocycle carbamates 7-12 can proceed by the three mechanisms discussed above (Scheme 1), depending on the basicity of the amine, the nature of the leaving group, the solvent used, and the classification of the N atom of the nonleaving group. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The mechanism based on the formation of the isocyanate was ruled out because carbamates 7-12 do not have hydrogen atoms, which are required for the elimination. The BAC 2 mechanism can proceed by a concerted mechanism (Scheme 1, pathway b) or stepwise mechanism in which the ratedetermining step is the formation of a tetrahedral intermediate or amine catalysis or the expulsion of the leaving group (Scheme 1, pathway a) in the rate-determining step.…”

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

“…It was found that a cyclic sulfinate ester (sultine) undergoes ring opening in an aqueous alkaline solution to give [ 18 O]‐sulfinate ion, after alkaline hydrolysis with H 2 18 O, while the cyclic sulfinate is stable in an acidic aqueous solution. Alkaline ring opening and the reverse ring closure in an aqueous acid solution of cyclic sulfinate esters have been studied extensively . Hydrolysis of a sulfinate ester is formally similar to that of a carboxylate ester (Scheme a).…”

Aminolysis of Methylbenzene Sulfinate: Definitive Evidence for a Stepwise Mechanism

“…1-2 For example, the acid hydrolysis of alkyl sulfinate esters as well as cyclic sulfinates proceeds in a concerted SN2 type mechanism, [3][4] while the base catalyzed hydrolysis of cyclic sulfinates with a phenolic leaving group takes place through a hypervalent intermediate. 5 However, there is little report on the aminolysis of sulfinate esters.…”