Efficient route to benzo[4,5]imidazo[2,1-a]phthalazines

Benzo4,5]imidazo2,1-a]phthalazines have been obtained from various o-nitrophenylhydrazines through different 2-(2-nitrophenyl)-1,2-dihydro-1-phthalazinones as intermediates using an elaborated advanced procedure. An activated chlorine atom in 2-nitrophenyl moiety of the latter is able to undergo nucleophilic substitution for secondary alicyclic amines yielding novel substituted phthalazinones. Their one-pot reduction and cyclodehydration yield a series of novel substituted benzo4,5]imidazo2,1-a]phthalazines.