Quinoidal Tetrazines:  Formation of a Fascinating Compound Class, Beatrix Bostai, Zoltán Novák, Attila C. Bényei, András Kotschy, Org. Lett. 2007, 9, 3437-3439. DOI: 10.1021/ol701442h | [Full Text Link] [Supp. Info Link, CIF]

A series of different N-heterocyclic carbenes (NHCs) were reacted with 3,6-bis(3‘,5‘-dimethylpyrazolyl)-tetrazine in the presence of an inorganic carbonate to provide access to a hitherto unprecedented compound class. The formed tetrazine derivatives bearing the NHC in the 3-position and an oxygen in the 6-position show a quinoidal-like structure, according to physical examinations and X-ray crystallography.