Formation of σ-anionic complexes in reactions between 5-nitrothiazole, 6-nitrobenzothiazole and tetrabutylammonium borohydride

Abstract

The title reactions were performed in toluene, tetrahydrofuran (THF) and dimethylsulfoxide. ¹H NMR spectral data from the reaction mixtures in Me₂SO and in THF indicate that each substrate affords only one respective σ-anionic complex. Kinetic data on formation of the complexes indicate that the attack of the nucleophile and stability of the complexes are affected greatly by changing the solvent. In agreement with our previous findings, in Me₂SO the rate of formation of the complexes from both substrates considered is lower than that observed in less polar solvents (toluene and THF). The explanation of this trend includes comparison of charge dispersion in the transition state with respect to the initial state and the possibility of changes in the hydride ion carrier when the solvent is changed.