1,4‐Addition of TMSCCl3 to Nitroalkenes: Efficient Reaction Conditions and Mechanistic Understanding

Improved synthetic conditions allow preparation of TMSCCl₃ in good yield (70 %) and excellent purity. Compounds of the type NBu₄X [X=Ph₃SiF₂ (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4‐additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (¹H, ¹⁹F, ¹³C and ²⁹Si) under anaerobic conditions indicate that addition of TMSCCl₃ to TBAT (both 0.13 M ) at ?20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me₃SiF, Ph₃SiF and NBu₄CCl₃. The latter is stable to at least 0 °C and does not add nitroalkene from ?20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl₃ (both 0.13 M at ?20 °C), when treated with TBAT, leads to immediate formation of the 1,4‐addition product, suggesting the reaction proceeds via a transient [Me₃Si(alkene)CCl₃] species, in which (alkene) indicates an Si???O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl₃^? addition to the nitroalkene. This is demonstrated by the fact that isolated NBu₄[CH₂?NO₂] is an efficient promoter. Use of H₂C?CH(CH₂)₂CH?CHNO₂ in air affords radical‐derived bicyclic products arising from aerobic oxidation.