Enantioselective organo-SOMO activation enables radical based functionalization of carbonyl compounds.

Five isatin anions were prepared by deprotonation of initial isatins in aprotic solvents using basic fluoride and acetate anions (F− and CH3COO−). The F− basicity is sufficient to deprotonate isatin NH hydrogen from all the studied compounds. This process is reversible. In the presence of proton donor solvents, the anions form the corresponding isatins. The isatin hydrogen acidity depends on the overall structure of the isatin derivatives. The anions were characterized by ultraviolet–visible (UV–Vis), Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Interestingly, the anions form aggregates at concentrations above 10−3 mol·dm−3. Further, the effect of cations on the UV–Vis spectra of the studied anions was studied. Charge transfer and its distribution in the anion depends on the radius and the cation electron configuration. The alkali metal cations, tetrabutylammonium (TBA+), Mg2+ and Ag+, interact with the C-2 carbonyl oxygen of the isatin anion. The interaction has a coulombic character. On the other hand, Cd2+, Zn2+, Hg2+, Co2+, and Cu+ cations form a coordinate bond with the isatin nitrogen.

Organocatalytic SOMO reactions can provide access to various α-functionalized carbonyl compounds. Chiral imidazolidinones catalysed the organo-SOMO reactions of aldehydes and ketones with cyclic and acyclic enol silanes. The resulting chiral dicarbonyl compounds were obtained in yields of up to 80% and enantiomeric purities of up to 90% ee. Under the SOMO conditions, silyl ketene acetals did not afford the desired products. However, silyl ketene thioacetal could be employed, and the corresponding product was isolated with useful enantiomeric purity of 82% ee.

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