Tetrazines, literature reviews

Of the three possible tetrazine systems the 1,2,3,5-tetrazines (24), also called as-tetrazines, are by far the least studied class. No compound with this structure was mentioned in the last review <78HC(33)1296), which covered the literature through Chemical Abstracts 1974. The parent compound has structure (24) and is numbered as indicated. 

A number of excellent reviews on the 1,2,4,5-tetrazines (39) have been published. The first, by Wiley in 1956 (56HC(10)179), covered the literature through Chemical Abstracts 1950 a second, by Wystrach, appeared eleven years later (B-67MI22101), and finally in 1978 Wiley comprehensively reviewed the whole literature through Chemical Abstracts 1978 (78HC(33)1075). Since that time about 350 publications dealing with physical, chemical or biochemical aspects of the 1,2,4,5-tetrazines have been covered by Chemical Abstracts. 

Reaction of aldehydes with hydrazine, or mono- or 1,2-disubstituted hydrazines is the method used almost exclusively for the preparation of hexahydro-l,2,4,5-tetrazines (377). All types of hydrazines have been used hydrazine itself, monoalkyl-, monoaryl-, dialkyl-, diaryl-, alkylaryl-, alkylacyl- or arylacyl-hydrazines. The aldehydes used were mainly aliphatic aldehydes. An excellent review by Wiley of the literature on this reaction up to 1974 is available (78HC(33)1075, p. 1190). 

Until now, no fully aromatic monocyclic 1,2,3.4-tetrazine has been synthesized, but a great many theoretical calculations have been published on this system. Contrary to this, a great number of dihydro- and tetrahydro-l,2,3,4-tetrazines are known. Reviews on the dihydro- and tetrahydro-l,2,3,4-tetrazines can be found in the literature.1-4... 

For a long time, 1,2,3,5-tetrazines were the least studied class of the three possible tetrazine systems. Until 1983. only three research articles dealing with the chemistry of 1,2,3,5-tetrazines had been published. In other articles theoretical calculations of this system were presented. The literature until 1983 has been discussed in two reviews.1,2... 

Section 6.21.5.9 on redox reactions discusses the formation of radical cations and radical anions from tetrazines, dihydrotetrazines, and tetrahydrotetrazines. The literature cited there offers all information on relevant ESR investigations in this field. Earlier literature is to be found in Neun-hoeffer s review <84CHEC-i(3)540>. 

Many detailed procedures for the synthesis of specific compounds can be extracted from the schemes presented above and the corresponding literature of these contributions. A review describes tetrazine synthesis using carboxylic iminoesters <95RCR317>. 

Structure 14, a furazano-l,2,3,4-tetrazine 4,6-dioxide, although prepared previously, was reported in the literature during the period covered in this review <1995MC227>. The tricyclic l,2,3,4-tetrazino[5,6-/ -l,2,3,4-benzotetrazines 15 were reported in 1999 <19970L721>. Structures 16 are tetrahydro-l,2,3,4-tetrazines, with R being a carbohydrate moiety <1999JOC6297>. 

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