Stereochemistry of hydrogen–deuterium exchange α to the sulphinyl group in 2H-naphtho[1,8-bc]thiophen derivatives

Abstract

The rate of deuterium exchange in MeONa—MeOD of α-protons having an equal stereochemical relation to a sulphinyl group was found to follow an opposite trend in 2H-naphtho[1,8-bc]thiophen derivatives (6)–(8) to that previously observed in 2-thiabicyclo[2.2.1]heptane derivatives (1) and (2), for which tetrahedral α-sulphinyl carbanions of different stability had been proposed as intermediates in the exchange process. The experimental results were rationalized by assiging to tetrahedral and planar α-sulphinyl carbanions a separate role in determining, according to their relative stability, the rate of proton abstraction or the stereochemistry of the exchange, or both.