2007 Rediscovery
In 2006 and again in 2007 the Zincke reaction was rediscovered by a research group from Japan and a group from the USA. Both groups claimed the synthesis of a 12 membered diazaannulene (structure 1) from an N-aryl pyridinium chloride and an amine, an aniline in the case of the Japanese group (depicted below) and an aliphatic amine (anticipating surfactant properties) in the case of the American group.
In a letter to Angewandte Chemie, the German chemist Manfred Christl pointed out not only that the alleged new chemistry was in fact 100 year old Zincke chemistry but also that the proposed structure for the reaction product was not the 12 membered ring but the 6 membered pyridinium salt (structure 2). Initially both groups conceded that they had ignored existing literature on Zincke but held on to the annulene structure based on their electrospray ionization (ESI) results which according to them clearly showed dimer. In his letter Christl remarked that in ESI measurements association of molecules is a common phenomenon. In addition, he noted similarities in melting point and NMR spectroscopy.
As of December 2007 the Japanese group retracted its paper in Organic Letters due to uncertainties regarding what products are formed in the reaction described and the US group added a correction to theirs in the Angewandte Chemie stating they wish(ed) to alter the proposed structure of (the) annulene. The issue did receive some media coverage:
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