Differentiation between Enamines and Tautomerizable Imines in the Oxidation Reaction with TEMPO
Weiping Su and Wei Zhuang report on the differentiation between enamines and tautomerizable imines.
Imines and enamines are ubiquitously encountered intermediates in organic synthesis, especially in recently developed aminocatalysis reactions for the efficient and selective functionalization of aldehydes and ketones. Imines featuring α-hydrogens are in equilibrium with their enamine tautomers. This imine–enamine tautomerism is the nitrogen analogue of keto–enol tautomerism, but with higher reactivity. This feature makes the tautomerizable imine resemble the reactivity of the corresponding enamine in organic transformations. Although several examples have been reported on the utilization of this tautomerizable character of imines for organic synthesis, the exact difference in reactivity between the imine-derived enamine tautomer and the real enamine remains underdeveloped. In light of this, the research groups of Professor Weiping Su and Wei Zhuang at Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences (P. R. of China) collaborated to develop a unique model reaction pattern that could discriminate this subtle discrepancy, affording molecular diversity depending on the chemistry of imine and enamine tautomers and offering an insight into their structure–reactivity relationship.