Multivariate Optimization and Mechanistic Considerations of the Amine Induced Ring-Opening Reaction of 2-Alkyl-3-bromo-5-methylthiophene-1,1-dioxides

In the optimization of the ring-opening reaction of thiophene-1,1-dioxides, 3-bromo-2,5-dimethylthiophene-1,1-dioxide (1) and 2-(2-hydroxyethyl)piperidine (7) were chosen as model reagents. Solvent, temperature, molar ratio between amine and dioxide and the amount of solvent were variables included in the optimization. A central composite design was chosen for the investigation and a canonical analysis of the response sur face was performed. When reacting 3-bromo-2-isopropyl-5-trideuteriomethylthiophene-1,1-dioxide (23) with 7 a primary kinetic isotope effect, diminished by internal return, was found for the initial proton abstractions as well as an intramolecular deuterium transfer in the tautomerization of 23.