Azolo[1,4]diazepines: the methods of synthesis and structural modification
The literature relating to the methods of synthesis and chemical transformations of azolo[1,4]diazepines (pyrazolo-, imidazo-, triazolo-, isoxazolo-, oxazolo-, isothiazolo- and thiazolodiazepines) currently known have been generalized and systematized. Their role as important substances for the design of compounds with a great pharmacological potential has been noted. The methods of synthesis of pyrazolo[3,4-e][1,4]diazepines, pyrazolo[4,3-e][1,4]diazepines and tri- and tetracyclic pyrazolo[1,4]diazepines based on formation of the diazepine ring in most cases due to transformations of multifunctional pyrazole derivatives have been described in detail. A significant emphasis is focused on the structural functionalization of pyrazolo[1,4]diazepines; this functionalization is a powerful tool to design attractive synthetic and biological derivatives. On the examples of 7-hydroxypyrazole[3,4-e][1,4]diazepines the effect of the reaction conditions, electronic and steric parameters, which control the processes of functionalization of the diazepine nucleus with SH-, NH- and C- nucleophilic reagents, is described. The synthetic potential of 7-arylpyrazole[4,3-e][1,4]diazepin-4-ones as key structures for their direct functionalization in position 4 with chloro-, methylthio-, amino- and hydrazino groups is shown. The methods of preparation and some chemical transformations of imidazo[1,4]diazepines, in particular imidazo[4,5-e][1,4]diazepin-8-ones and 5,8-diones, which in recent years attract great attention of researchers, have been analyzed.