Organophotocatalytic dearomatization of indoles, pyrroles and benzo(thio)furans via a Giese-type transformation
Dearomatisation of indoles allows efficient access to indolines, but often is incompatible with electron-withdrawing substituents. Here a photoredox Giese-type dearomatisation of indoles yields 2,3-disubstituted indolines bearing electron-withdrawing groups. Accessing fascinating organic and biological significant indolines via dearomatization of indoles represents one of the most efficient approaches. However, it has been difficult for the dearomatization of the electron deficient indoles. Here we report the studies leading to developing a photoredox mediated Giese-type transformation strategy for the dearomatization of the indoles. The reaction has been implemented for chemoselectively breaking indolyl C=C bonds embedded in the aromatic system. The synthetic power of this strategy has been demonstrated by using structurally diverse indoles bearing common electron-withdrawing groups including (thio)ester, amide, ketone, nitrile and even aromatics at either C-2 or C-3 positions and ubiquitous carboxylic acids as radical coupling partner with high trans-stereoselectivity (>20:1 dr). This manifold can also be applied to other aromatic heterocycles including pyrroles, benzofurans and benzothiophenes. Furthermore, enantioselective dearomatization of indoles has been achieved by a chiral camphorsultam auxiliary with high diastereoselectivity.
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Reference:
Indole alkaloid derivatives as building blocks of natural products from Bacillus thuringiensis and Bacillus velezensis and their antibacterial and antifungal activity study,
,Preparation of Indole Containing Building Blocks for the Regiospecific Construction of Indole Appended Pyrazoles and Pyrroles