Photoinduced Chloroamination Cyclization Cascade with N-Chlorosuccinimide: From N-(Allenyl)sulfonylamides to 2-(1-Chlorovinyl)pyrrolidines

Abstract

Here, we present an intriguing photoinduced chloroamination cyclization of allenes bearing a tethered sulfonylamido group to afford 2-(1-chlorovinyl)pyrrolidines and related heterocycles in the presence of N-chlorosuccinimide (NCS) as the chlorine source. An in depth experimental and computational mechanistic study revealed the existence of multiple reaction pathways leading to a common nitrogen centered radical (NCR). This key NCR can be, in fact, originated from (a) the oxidation of the deprotonated allene by the photoexcited state of the Ru-catalyst and (b) the photodissociation of the in situ formed N-chloroallene. The NCR formation triggers an intramolecular cyclization to a highly reactive pyrrolidine vinyl radical, which upon chlorination delivers the final product. Thus, NCS plays a dual role, serving both as an activator of the sulfonamido functionality and as the chlorinating agent.

Radical Cyclization-Initiated Difunctionalization Reactions of Alkenes and Alkynes

“…In 2023, Renzi and coworkers reported a photo-induced radical reaction of N -(allenyl)sulfonylamides for the synthesis of 2-(1-chlorovinyl)pyrrolidines. The blue LEDs irradiated reactions of N -(allenyl)sulfonylamides 202 , N -chlorosuccinimide (NCS) and K 2 CO 3 under the catalysis of [Ru(bpy) 3 ](PF 6 ) 2 using anhydrous PhCH 3 and HCO 2 CH 3 as a co-solvent for 21 h gave products 2-(1-chlorovinyl)pyrrolidines 203 in good yields ( Scheme 45 ) [ 70 ]. After the initial deprotonation of allenes 202 with a base to form 204 , there are two different pathways for the formation of radicals N -centered radicals 205 .…”

Visible light-mediated halogenation of organic compounds

“…Another visible-light induced method for allene transformation relies on an intramolecular cyclative aminochlorination. 83 Allenes 57 , containing a sulfonamide moiety, could participate in a Ru(bpy) 3 (PF 6 ) 2 -catalysed reaction with NCS in a toluene-methylformate mixture under nitrogen atmosphere (Scheme 35). Potassium carbonate was used in catalytic amounts.…”

Nitrogen-Centered Radicals Derived from Azidonucleosides

“…They are generated via homolytic cleavage, reductive/oxidative conditions, and proton-coupled electron transfer (PCET) methods [4,5,7,8]. Precursors to NCRs include N-halogenated amines [9,10], aryloxyamides [11], sulfonylamides [12], or O-aroyloximes [13], among others [4,8]. NCRs generated from azides (R-N 3 ) are important due to the synthetic ease of the incorporation of azido groups into the frame of complex molecules, including natural products and their versatile application to the subsequent functionalization reactions [14,15].…”