Gas-Phase Anionic σ-Adduct (Trans)formations in Heteroaromatic Systems(1)

Anions of nitroderivatives of thiophene and furan were subjected to the reactions with selected C-H acids in the gas phase. Various structures and reaction pathways were proposed for the observed ionic products. In general, the reactions of heteroaromatic anions with C-H acids may be divided into three groups, depending on the proton affinity difference between C-H acid’s conjugate base and heteroaromatic anion (ΔPA). The proton transfer from C-H acid to heteroaromatic anion is a dominant process in the reactions for which ΔPA < 0 kcal mol(−1), whereas the reactions with high ΔPA (ΔPA > 16 kcal mol(−1)) do not lead to any ionic products. The formation of σ-adducts and products of their further transformations according to the VNS, S(N)Ar, cine, and tele substitution mechanisms have been proposed for reactions with moderate ΔPA. The other possible mechanisms as S(N)2 reaction, nucleophilic addition to the cyano group, ring-opening pathway, and halogenophilic reaction have also been discussed to contribute in the reactions between heteroaromatic anions and C-H acids. [Figure: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s13361-015-1122-1) contains supplementary material, which is available to authorized users.