XtalFluor‐E Enabled Regioselective Synthesis of Di‐Indole Sulfides by C3−H Sulfenylation of Indoles

Abstract

A simple, regioselective synthesis of di‐indole sulfides by electrophilic aromatic substitution of the C3‐position of indoles was achieved using Xtalfluor‐E as the sulfenylating reagent. The addition of amine bases was found to have a significant effect on the reaction outcome, with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) switching off the reactivity of XtalFluor‐E, while the hindered base 2,6‐ditertbutyl‐4‐methylpyridine (DBP) led to the formation of two di‐indole‐sulfur containing products, one S(II) and one S(IV). The optimal base for accessing the di‐indole sulfides in high yield proved to be Hünigs base, EtNiPr2. While this amine formed a Lewis adduct with XtalFluor‐E, adduct formation did not completely quench electrophilic reactivity indicating reversible coordination to the sulfur center. This is the first report utilizing XtalFluor‐E in electrophilic aromatic substitution to form C−S bonds to our knowledge, and this process is applicable to a wide range of functionalized indoles and does not require N1‐protection.