Larisa V. Politanskaya

The Influence of Nucleophile Substituents on the Orientation in the Reaction between 2,4-Difluoronitrobenzene and Lithium Phenoxides in Liquid Ammonia

The dependence of the orientation of aryloxydefluorination of 2,4-difluoronitrobenzene (1) (o/p ratio) by the action of X-substituted lithium phenoxides 2 (X = p-OMe, p-Me, p-Et, p-iPr, p-tBu, m-Me, H, p-F) in liquid ammonia in the temperature range from −55 to −35 °C has been investigated. The enthalpic preference for ortho-fluorine substitution decreases with weakening substituent electron-donating capability in the order: p-OMe > p-Me ≈ p-Et > m-Me > H ⩾ p-F. The predominant fluorine substitution at the ortho position for X = p-Me, p-Et turns into a preference for substitution at the para position when X = p-iPr, and this increases further on going to X = p-tBu. PM3, AM1 and MNDO MO calculations showed greater stability of the intermediate anionic σ-complexes formed on nucleophile addition at the para position, thus suggesting that the predominant ortho substitution manifested for X = p-OMe, m-Me, H, p-F and p-Alk = Me, Et is due to control over orientation by the charge distribution in the substrate. The substrate electronic structure, as a controlling factor, is probably changed by the relative stability of intermediate anionic σ-complexes on going to p-Alk = iPr, tBu, as a consequence of an enhancement of the substituent’s electron-withdrawing nature with the increase in alkyl group polarizability in the order: p-Me ≈ p-Et < p-iPr < p-tBu.

Molecular and Crystal Structure of 2-Amino-Polyfluorophenyl-4,4,5,5-Tetramethyl-4,5-Dihydro-1H-Imidazol- 3-Oxide-1-Oxyls

By cross-coupling of 2-iodo-polyfluoroanilines with a [AuPPh3NN] complex (where NN is 4,4,5,5- tetramethyl-3-oxide-1-oxyl-2-imidazolin-2-ide) in the presence of [Pd(PPh3)4], nitroxide radicals (2-aminopolyfluorophenyl- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyls) are synthesized. Their molecular and crystal structures are determined by the X-ray crystallographic analysis. It is shown that in the solid phase there are both intra- and intermolecular hydrogen bonds between NH2 groups and O atoms of paramagnetic fragments, which link the molecules into chains or dimers.