Semiramis Ayral-Kaloustian

Two Efficient Methods for Replacement of Sulfur by Oxygen in a Thionolactone

Abstract Selective methods for conversion of thionoesters or thiono-lactones to the corresponding ordinary esters or lactones through replacement of sulfur by oxygen are generally lacking, apart from the long known reaction using aqueous silver nitrate1 and related processes with lead1 or mercury2 carboxylates. Our recent preparation of bicyclic thionolactone 1 3 affords a convenient substrate for examination of possible reagents for this transformation. A particularly useful property of 1 is that tetrahedral intermediates 2 and 3, formed on nucleophilic addition of Nu− to 1, have a stereoelectronically favored3,4 pathway for cleavage of the lactone bridge. Such cleavage in 1 is effectively irreversible, since it will be quickly followed by inversion to the stable diequatorial conformer of cis-3-hydroxycyclohexaneacetic acid (4) or an appropriate derivative, depending on the specific nature of Nu−. This feature makes 1 a sensitive test of methods for replacement of sulfur by oxygen without competing ruptu...