Reductive Cleavage of Sulfones and Sulfonamides by a Neutral Organic Super-Electron-Donor (S.E.D.) Reagent

摘要

The sulfonyl group finds extensive applications in organic and medicinal chemistry both in sulfonamides, popular as robust protecting groups for amines, and in sulfones. Frequently, sulfones are introduced into synthetic schemes to assist particular transformations; further progress along the synthetic route can later require the removal of a sulfone group, and this can be achieved by reductive desulfonylation or, in the special cases of α-halo- or β-acyloxysulfones, by elimination to an alkene. For reductive removal of sulfones and for reductive cleavage of classic sulfonamides, different methods use alkali metals (Li, Na, K), lithium naphthalenide, SmI_2 with HMPA, or LiAlH_4 in the presence of nickel compounds. All these reduction methods are mediated by highly aggressive metal-containing reducing agents. Electrochemical reduction is also used for the reductive cleavage of aryl sulfones (ArSO_2R) and sulfonamides. With typical reduction potentials of —2.3 V, they pose some of the greatest challenges in functional group reduction.