Photochemical pincer-catalyzed reductive cyclisation towards indolines and oxindoles

Area of Science:

• Organic Chemistry
• Photocatalysis
• Synthetic Methodology

Background:

• Traditional syntheses of indolines and oxindoles often rely on expensive iridium or gold catalysts.
• Previous methods typically involve the cleavage of carbon-iodine (C-I) or carbon-bromine (C-Br) bonds as the initial step.
• There is a need for more sustainable and efficient synthetic routes to these important heterocycles.

Purpose of the Study:

• To develop a novel organophotocatalytic method for the synthesis of indolines and oxindoles.
• To utilize readily available starting materials and mild reaction conditions.
• To demonstrate an atom-economic approach using a trifunctional reagent.

Main Methods:

• Employing an organophotocatalyst, specifically a pincer ligand, capable of acting as a potent reducing agent upon deprotonation.
• Utilizing unusual substrates: α-chloro amides and N-(2-chlorophenyl)-N-alkyl methacrylamides.
• Initiating the reaction via reductive cleavage of the carbon-chloride (C-Cl) bond.

Main Results:

• Successful synthesis of indolines and oxindoles under mild reaction conditions.
• Achieving the desired heterocycles through a sequence of C-Cl bond cleavage, 5-exo-trig ring cyclization, and hydrogen atom abstraction.
• Demonstrating the trifunctional role of potassium tert-butoxide (KOtBu) in an atom-economic manner.

Conclusions:

• The developed organophotocatalytic method provides a significant advancement over existing synthetic strategies for indolines and oxindoles.
• This new method offers a milder, more sustainable, and efficient alternative, avoiding the need for precious metal catalysts.
• The study highlights the versatility of the photocatalyst and the atom-economic utility of KOtBu.