Reactions performed in DMSO-d6 rule out the possibility that DMSO is involved in a HAT process, as product 3ea was formed as sole product, without any sign of deuteration (Figure , III.1). Herein the formation of the carbanion is more plausible. This hypothesis was further proved when the reaction was performed under a CO2 atmosphere. Herein, compound 5a was obtained in 45% yield which constitutes a strong indication that the reaction proceeds through nucleophilic attack of CO2 by the anionic