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

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. Hydrogen bonds go photoredox: The binding motif of template A was shown to be compatible with the generation of α‐aminoalkyl radicals by ruthenium‐catalyzed photoelectron transfer. The prostereogenic center in 3‐alkylidene indolin‐2‐ones was attacked with significant selectivity reaching up to 72 % ee (see scheme).