Molecular rearrangements Dimroth rearrangement

Diazotization of 5-amino[l, 2,3]triazole 692 afforded (88BSB179) triaz-olo[l, 5-i>][l, 2,4]triazine 694 as a result of a Dimroth rearrangement of the initially formed isomeric structure triazolo[5,l-c][l,2,4]triazine 693. Molecular structure of 694 was determined by single X-ray diffraction (Scheme 146). 

In the reactions described in Section III,C, a three-atom fragment in the heterocycle is replaced by the same atoms of the reagent and with the same sequence of atoms. This type of reaction has been referred to as an inter-molecular transfragment reaction (67JA6911) and therefore can be clearly distinguished from molecular rearrangements, such as the Dimroth reactions (68MI1 see also Chapter IV) and photochemical transposition reactions. 

Based on the experience mentioned previously, the Dimroth rearrangement was succesfully applied for the preparation of water-soluble macro-molecular adenosine derivatives of the redox enzymes 72 (NAD(H), NADP(H), and FAD) (Scheme IV.31) (86MI1 87MI3, 87MI2 88H1623 89MI1 90M11). 

A symmetrical tricyclic 1,3,6-thiadiazepine derivative 152 (Scheme 48) has been synthesized [68,69] in 54% yield starting from 5-bromo-thiadiazole derivative 144 and 1,2-diaminobenzene 145. The synthesis embraces two types of molecular rearrangements Smiles and Dimroth s. 

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