Synthesis of structurally diverse silicon-incorporated indolines via silyl radical-triggered radical cascade reactions

A silyl radical-triggered radical addition-translocation-cyclization (RATC) process followed by chemo-divergent conversions was developed to construct structurally diverse silicon-incorporated indolines. The reaction proceeds via a sequence of silyl radical addition, 1,5-hydrogen atom transfer (HAT), and cyclization, leading to an indoline framework. The resulting alpha-silyl carbon radical intermediate subsequently undergoes varied reactions through tuning the substituents attached to this radical centre. Secondary radicals undergo an exclusive hydrogen atom transfer reaction, while the introduction of a methoxycarbonyl group leads to an unusual radical 1,4-silyl migration. Interestingly, for alkyl-substituted tertiary radicals, an oxidation/deprotonation process takes place preferentially, giving alkene-tethered products. These chemo-divergent reactions provide facile access to structurally diverse silicon-modified indolines from simple starting materials. Further transformations to produce synthetically useful building blocks are also demonstrated.