Enantioselective Visible‐Light‐Induced Radical‐Addition Reactions to 3‐Alkylidene Indolin‐2‐ones

Abstract

The title compounds underwent a facile and high-yielding addition reaction (19 examples, 66-99% yield) with various N-(trimethylsilyl)methyl-substituted amines upon irradiation with visible light and catalysis by a metal complex. If the alkylidene substituent is non-symmetric and if the reaction is performed in the presence of a chiral hydrogen-bonding template, products are obtained with significant enantioselectivity (58-72% ee) as a mixture of diastereoisomers. Mechanistic studies suggest a closed catalytic cycle for the photoactive metal complex. However, the silyl transfer from the amine occurs not only to the product, but also to the substrate, and interferes with the desired chirality transfer.

Triplet Energy Transfer from Ruthenium Complexes to Chiral Eniminium Ions: Enantioselective Synthesis of Cyclobutanecarbaldehydes by [2+2] Photocycloaddition

“…Ru(bpz) 3 (PF 6 ) 2 suffered protonation under these conditions and could not be used. To our delight, Ru(bpy) 3 X 2 turned out to be a competent catalyst and was employed either as hexafluorophosphate (X=PF 6 ) or as tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (X=BArF) salt. Like Ru(bpz) 3 (PF 6 ) 2 , Ru(bpy) 3 (PF 6 ) 2 did not show any significant background reaction, that is, it did not catalyze the direct conversion 6 a → rac ‐ 3 aa at λ =458 nm.…”

Triplet Energy Transfer from Ruthenium Complexes to Chiral Eniminium Ions: Enantioselective Synthesis of Cyclobutanecarbaldehydes by [2+2] Photocycloaddition

“…Ru-(bpz) 3 (PF 6 ) 2 suffered protonation under these conditions and could not be used. To our delight, Ru(bpy) 3 X 2 turned out to be a competent catalyst and was employed either as hexafluorophosphate (X = PF 6 ) or as tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (X = BArF) [35] salt. Like Ru-(bpz) 3 (PF 6 ) 2 , Ru(bpy) 3 (PF 6 ) 2 did not show any significant background reaction, that is, it did not catalyze the direct conversion 6 a !…”

Synthesis of β‐Substituted γ‐Aminobutyric Acid Derivatives through Enantioselective Photoredox Catalysis

“…However, current methods are limited to mainly aryl‐substituted amines (Figure a). For example, Yoon and co‐workers employed aromatic tertiary α‐silylalkyl amines as radical precursors under Ru‐photoredox conditions and combined it with a Sc‐catalyzed enantioselective conjugate addition . Melchiorre and co‐workers reported a dual photoredox/organo catalysis system as an approach to β‐substituted GABA analogues, but substrates are limited to aromatic tertiary amines and to cyclic enones .…”