Resumen de Probing the Reactivity of Dimethylsulfoxonium Methylide with Conjugated and Nonconjugated Carbonyl Compounds:: An Undergraduate Experiment Combining Synthesis, Spectral Analysis, and Mechanistic Discovery

James A. Ciaccio, Elena L. Guevara, Rabeka Alam, Christina D. D'agrosa

• We introduce students to dimethylsulfoxonium methylide (DMSY) epoxidation of aryl and nonconjugated aliphatic aldehydes and ketones without revealing that DMSY cyclopropanates enones by Michael-initiated ring closure (MIRC). Each student performs the reaction of DMSY with one of nine carbonyl compounds, including four enones, and then analyzes the 13C NMR and IR spectra of their reaction product in comparison with spectra of their carbonyl substrate. The spectra of products from aryl and nonconjugated aldehydes and ketones show the expected absence of a carbonyl peak and the addition of two upfield 13C peaks (indicating carbonyl epoxidation), whereas spectra of products from enones unexpectedly (to the student) display a carbonyl peak, no alkene 13C peaks, and three (instead of two) additional upfield 13C peaks. Identification of the latter products as cyclopropyl ketones leads to a discussion of conjugate addition and MIRC, and it stresses the avoidance of making false assumptions regarding the outcome of chemical reactions.