Unraveling the Role of Supramolecular Additives in a Proline‐Catalyzed Reaction.

Various additives, typically based on molecules featuring H‐bond donor motifs, have been essayed towards improving the catalytic properties of proline. However, their mode of action is not clear yet. By employing in situ 1H and 19F NMR DOSY experiments, the role of a tetrafluoroborate guanidinium salt in a novel proline‐catalyzed cross‐aldol reaction between α,α‐dichloroacetone and aromatic aldehydes has been fully disclosed. The cooperative participation of a TBD‐derived guanidinium salt and proline promotes the cross‐aldol reaction between α,α‐dichloroacetone and aromatic aldehydes. NMR DOSY experiments allow disclosing the mode of action of this additive, which operated through H‐bonding interactions. [ABSTRACT FROM AUTHOR]