RING-OPENING AND CLOSURE AND OXYGEN-ISOTOPE EXCHANGE OF CYCLIC SULFINATE ESTERS

Alkaline ring opening and the reverse ring closure in an aqueous acid solution of cyclic sulfinate esters (sultines), 3H-2,1-benzoxathiole 1-oxide (1a) and 3,4-dihydro-2,1-benzoxathiin 1-oxide (1b), have kinetically been studied at 25 degrees C. The sultine 1a is more reactive than 1b in both the opening and closure reactions. However, acid-catalyzed oxygen isotope exchange of the O-18-labeled sultine 1a was found to be slower than that of the labeled 1b. The contrasting reactivities of the five- and six-membered sultines in at alkaline and acid solutions as well as the reaction mechanisms are considered on the basis of the ab initio molecular orbital calculations.