The Reaction of 9‐Bromoanthracene with Benzenethiolate Anion in Tetraglyme: Evidence against a competing electron‐transfer mechanism

Abstract

The reaction of 9-bromoanthracene (1) with benzenethiol(ate) in tetraglyme proceeds by a SNAr mechanism. The concurrent formation of anthracene is not due to a competing single-electron-transfer pathway involving either benzenethiol or benzenethiolate anion.The involvement of single-electron-transfer (SET) pathways in organic chemistry is a topic of fundamental importance (for reviews, see [l]). The occurrence of chain mechanisms involving radical anions for the substitution of both alkyl and aryl halides, the S,,1 mechanism, was delineated [2]. Quite recently, however, a mechanistic reappraisal of the involvement of aryl 0 radicals in the S,,1 substitution of aryl halides appeared [3a] (for references to the S,,2 mechanism, see [3b]).The substitution of 9-bromoanthracene (1) with sodium benzenethiolate (2a) in the solvent tetraglyme ( = 2,5,8,11,14-pentaoxapentadecane) gave, besides te expected substitution product 9-(pheny1thio)anthracene (3), the reduction product anthracene (4) [4] [5] (see Scheme). It was reasonably suggested that the formation of 4 was the result of a SET

Nucleophilic Substitution Reactions by Electron Transfer

“…ArN 2 F 4 B can be substituted in DMSO at room temperature (Tables and ). In some systems and depending on the experimental conditions, a competition between ET and the S N Ar mechanisms has been proposed for the reaction with PhS - ions 50 Photostimulated Reaction with PhS - Ions in Liquid Ammonia a Electrochemical initiation in DMSO or MeCN.…”

“…5-Chloro-6-nitroquinoxaline reacts with p -MeC 6 H 4 S - ions in MeOH to give disubstitution in 56% yield. In this reaction, which is proposed to take place by the S RN 1 mechanism, both the NO 2 and the Cl act as leaving groups 555b…”