Tris(4-bromophenyl)aminium Hexachloroantimonate as a “Waste-Utilized”-Type Initiator-Promoted C–H Chlorination via C–H Activation Relay: Synthesis of Chlorinated Pyrroles

Abstract

Using tris(4-bromophenyl)aminium hexachloroantimonate as a "waste-utilized"-type initiator, the aerobic oxidation of the sp 3 C−H bond of proline esters was realized via C−H activation relay, giving a series of halogenated pyrroles in high yields. The mechanistic study revealed that the counterion, SbCl 6 − , was involved in the radical chlorination process, which provides a new way to understand the role of the counterions.

C−H Bond Activation Relay (CHAR) of Proline Ester Derivatives Promoted by In Situ Triarylamine Radical Cation: Selective Synthesis of 4‐Bromopyrrole Derivatives

“…Based on the control experiments (Schemes 4 and 5) and our previous research, [6c] a plausible reaction pathway was presented (Scheme 6). We speculated that a triarylamine radical cation would be formed initially by the treatment of CuBr 2 with tris(4‐bormophenyl)amine, which causes the oxidation of the active C−H bond adjacent to nitrogen, providing a radical intermediate A .…”

“…Using triarylamine radical cation (tris(4‐bromophenyl)aminium hexachloroantimonate, TBPA) as the initiator and its counter ion, SbCl 6 − , as the chlorine atom donor, a series of chlorinated pyrroles were obtained through CHAR [Eq. (3)] [6c] . However, two obvious limitations limit the application of this reaction in pyrrole synthesis.…”