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 ofN-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 formedN-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.