Synthesis and Selected Reactions of Hydrazides Containing an Imidazole Moiety

The preparation of two types of imidazole derivatives bearing a hydrazide group was achieved by treatment of the corresponding esters with NH 2 NH 2 ⋅H 2 O in MeOH at room temperature. In the case of 4‐(ethoxycarbonyl)‐1 H ‐imidazole 3‐oxides 3 , hydrazides of type 1 were formed with retention of the N ‐oxide structure ( Scheme 1 ). Interestingly, due to a strong H‐bonding, no deoxygenation of the N→O function could be achieved even by treatment of 3 with Raney ‐Ni. The second type, 2‐[(1 H ‐imidazol‐2‐yl)sulfanyl]acetohydrazides 2 , was obtained from 1 H ‐imidazole‐2(3 H )‐thiones 4 in two steps via S ‐alkylation with methyl bromoacetate, followed by treatment with NH 2 NH 2 ⋅H 2 O ( Scheme 2 ). An imidazole 7 , containing both types of hydrazide groups, was prepared analogously from ethyl 2,3‐dihydro‐2‐thioxo‐1 H ‐imidazole‐4‐carboxylate 4d ( Scheme 4 ). Both types of hydrazides, 1 and 2 , were transformed successfully to the corresponding acylhydrazones 8 and 9 , respectively ( Scheme 5 ). Furthermore, it has been shown that hydrazides of type 1 are useful starting materials for the synthesis of 1,2,4‐triazole‐3‐thiones 11 and 1,3,4‐thiadiazole‐2‐amines 12 , bearing an imidazole 3‐oxide moiety ( Scheme 7 ).