| Abstract
| - Dynamic NMR measurements of 8-(dimethylamino)-1-acetonaphthone 1 in neutral solutions reveala solvent dependency of the barrier to NMe group interchange similar to that reported for N,N-dimethylacetamide. Titrating 1 with TFA in solvents of varying donicities gives rise to equilibriummixtures of N-protonated aminoketone 2 and the O-protonated transannular addition product 3,the interconversion rate of which is slow on the NMR time scale at ambient temperature. Thepreference for O- or N-protonation is medium-dependent, the amount of N-protonated 2 increasingwith a decrease in the nucleophilicity of the solvent. The set of equilibria which govern the interconversion of 2 and 3 in the titration mixtures are identified and their equilibrium constants evaluatedfrom the NMR data. X-ray analysis of the crystalline trifluoroacetate salt of O-protonated 3 indicatesthat the transannular N···CO bond of 3 is formed to an extent of only 80%. The equilibriumdistribution of 2 and 3, paired with the tetrafluoroborate anion, depends on both the nucleophilicityand the polarity of the solvent. In PhNO2 the enthalpy change 3 → 2 amounts to 2.6 kcal/mol.
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