Anodic Reactivity of Alkyl S -Glucosides.

A voltammetric study of a series of alkyl and aryl S -glucosides unveiled the reactivity patterns of alkyl S -glucosides toward anodic oxidation and found noteworthy differences with the trends followed by aryl derivatives. The oxidation potential of alkyl S -glucosides, estimated herein from square-wave voltammetry peak potentials ( E p ), depends on the steric properties of the aglycone. Glucosides substituted with bulky groups exhibit E p values at voltages more positive than the values of those carrying small aglycones. This relationship, observed in all analyzed alkyl series, is evidenced by good linear correlations between E p and Taft's steric parameters ( E S ) of the respective alkyl substituents. Moreover, the role of the aglycone's steric properties as a primary reactivity modulator is backed by poor correlations between E p and the radical stabilization energies (RSEs) of the aglycone-derived thiyl radicals (RS•). In contrast, aryl glucosides' E p values exhibit excellent correlations with the aryl substituents' Hammett parameters (σ+) and the ArS• RSEs, evidencing the inherent stability of the reactive radical intermediate as the primary factor controlling aryl glucoside's electrochemical reactivity. The reactivity differences between alkyl and aryl S -glucosides also extend to the protective group's effect on E p . Alkyl S -glucosides' reactivity proved to be more sensitive to protective group exchange.