10.1021/ja1084749
The study conducted by Roland Appel, Nicolai Hartmann, and Herbert Mayr from the Department of Chemistry at Ludwig-Maximilians-Universit?t München, investigates the cyclopropanation reactions using sulfur ylides. It focuses on the rates of reactions between stabilized and semistabilized sulfur ylides with benzhydrylium ions and Michael acceptors, measured using UV-vis spectroscopy in DMSO at 20°C. The research establishes a correlation between the second-order rate constants (log k2) and the electrophilicity parameters (E) of the electrophiles, which aids in calculating the nucleophile-specific parameters (N and s) for the sulfur ylides. The findings indicate that the rate constants for cyclopropanation reactions with Michael acceptors align with those for carbocations, suggesting a stepwise mechanism with the initial nucleophilic attack being rate-determining. This study provides a quantitative approach to understanding sulfur ylide reactivity, which is crucial for predicting the scope and limitations of cyclopropanation reactions in organic synthesis.