Reaction of a highly spiro-activated electrophilic cyclopropane with pyridines; an unusual solvent effect on reaction rate

Abstract

The kinetics of the reaction of 3,3,10,10-tetramethyldispiro[5.0.5.1]tridecane-1,5,8,12-tetraone (1) with pyridine was studied in various pure solvents (protic and aprotic). Although this reaction afforded a polar zwitterion [the pyridinium β-oxoenolate derivative (2)], the solvent effect on the reaction rate was not as remarkable as that in the Menschutkin reaction; it was related to Gutmann's DN parameters rather than to the Dimroth–Reichardt E_T values. The multiparameter analysis approach according to the Krygowski–Fawcett model in aprotic solvents and the Taft–Kamlet model in protic solvents was successful, giving log k₂=–8.82 × 10^–3E_T– 17.4 × 10^–3DN– 3.36 (r= 0.927; n= 8) and log k₂=–0.734_α+ 0.162β– 3.15 (r= 0.941; n= 6), respectively, Mechanisms are discussed.