Photochemical pincer-catalyzed reductive cyclisation towards indolines and oxindoles

Abstract

An organophotocatalytic method has been described towards the synthesis of indolines and oxindoles starting from unusual α-chloro amide and N-(2-chlorophenyl)-N-alkyl methacrylamide substrates. This marks a notable improvement since the earlier syntheses utilized iridium and gold catalysts, and involved C–I or C–Br bond cleavage as the initial step. Our photocatalyst is a pincer ligand that can be easily deprotonated to make a very strong reducing agent. The reductive cleavage of the carbon–chloride bond, and subsequent 5-exo-trig ring cyclization, followed by hydrogen atom abstraction, prepare the desired heterocycles under very mild reaction conditions. An atom economic use of KO^tBu has been shown to demonstrate the unusual trifunctional role of the latter.