Substitution and ring closure reactions of phthalazine derivatives

Abstract

Abstract 1‐(Phenylthio)‐ and 1‐(hydroxycarbonylmethylthio)‐4‐methylphthalazines were prepared from 1‐chloro‐4‐methylphthalazines ( 1 ). A series of 2‐benzyl‐ and benzenesulphonyl derivatives was prepared from the corresponding halides and 4‐methyl‐1(2 H )‐phthalazinone ( 4 ). 4‐Methyl‐1(2 H )‐phthalazinthione ( 6 ) was substituted at SH group to give 1‐(benzylthio)‐ and 1‐(ethoxycarbonylmethylthio)‐4‐methylphthalazines, 7 and 8 respectively. Treatment of hydrazine hydrate with 8 produced 1‐hydrazino‐4‐methylphthalazine ( 10 ). However, when the latter compound was treated with 1 it gave 1,2‐bis‐(4‐methylphthalazinyl)hydrazine. Treatment of 10 with aromatic aldehydes in glacial acetic acid gave the corresponding 3‐phenyl‐ s ‐triazolo‐[3,4‐ a ]‐6‐methylphthalazines 13 . 1‐Hydrazino‐4‐methylphthalazine ( 10 ) underwent cyclization reactions with acetic anhydride, ethyl chloroformate, carbon disulphide, ethylformate, ethyl oxalate and with nitrous acid to give the corresponding triazolo‐, triazino‐ and tetrazolophthalazine compounds.