Unactivated alkylsulfinic acids as an alkyl radical source for the synthesis of 3,3-dialkylindolin-2-ones via an electron donor–acceptor complex†

Using unactivated alkylsulfinic acids as an alkyl radical source, a novel and highly practical visible-light-assisted synthetic methodology for the alkylation/annulation of a series of N-arylacrylamides into corresponding 3,3-dialkylindolin-2-ones has been developed. This approach does not require a photosensitizer or any metal reagents because the development of an electron donor–acceptor complex between alkylsulfinates and 2-isocyano-1,1′-biphenyl (catalytic electron acceptor) allows, under visible-light irradiation, the preparation of desired products in good yields. The mildness, gram-scale synthesizability, no need for the use of toxic organic solvents and a transition metal, as well as suitability for the synthesis of bioactive compounds (used as progesterone antagonists and anti-depressants) are a few noteworthy features of this procedure. Furthermore, alkylsulfinic acids are stable, safe, easy to handle, and readily available compared to other alkyl radical donors (like N-(acyloxy)phthalimides and Katritzky salts) reported in the literature.