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
Die Reaktion von kernsubstituierten Bis‐benzylseleniden (I) mit HNO3 liefert in Abhängigkeit von den Substituenten R1 bis R5 entweder Selenoxide (II) oder Benzylnitrate (III).
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