 Upon heating α-picolinic acid will spontaneously decarboxylate forming the so-called 'Hammick Intermediate' (2), which can be viewed as an aromatic ylide.In the presence of a strong electrophile, such as an aldehyde or ketone, this species will undergo nucleophilic attack faster than proton transfer.After nucleophilic attack intramolecular proton transfer yields the desired carbinol (4).