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)-1H-imidazole 3-oxides 3, hydrazides of type 1 were formed with retention of the Noxide 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-[(1H-imidazol-2yl)sulfanyl]acetohydrazides 2, was obtained from 1H-imidazole-2(3H)-thiones 4 in two steps via Salkylation 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-1H-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).
Helvetica Chimica Acta -Vol. 94 (2011) The authors thank PD Dr. L. Bigler (University of Zurich) for recording a series of HR mass spectra.