No abstract

Hydrogen, as well as the halogen atom, at the 4 or 5 position in some 5‐ and 4‐nitroimidazoles were displaced by various nucleophiles such as the amino, cyano, hydroxy, and alkoxy groups. The greater reactivity of the departing group in the 4 position, which was regularly observed, is ascribed to the double activating effect of the azo and nitro groups. Cyanide ion in alcoholic solution reacted peculiarly with both 4‐ and 5‐nitroimidazoles giving o‐cyanoazoxyimidazoles as the only products. In some of the nucleophilic displacements at the 4 position of 5‐nitroimidazoles the formation of intermediate S̀‐complexes was observed.

New synthesis of 11‐acyl‐5,11‐dihydro‐6H‐pyrido[2,3‐b][1,4]benzodiazepin‐6‐ones (42‐44) is reported. The crucial steps (Scheme VI) represented N‐oxydation of 1 (1A) to 35 (35A), facilitated ring‐closure of 36 into 37, its subsequent N‐α‐chloroacetylation to 38, aminolysis to 39‐41 (involving N‐O anchimeric assistance as depicted in 38A) and deoxygenation to 42‐44 (Scheme VII). The central intermediate 37 is also obtained on oxygenation of 2, a new synthesis of which was reported in the previous paper of this series [3]. Other attempts of cyclisation “from the top” or “from the bottom” (Scheme I) are described. Thus, interaction of 1 with acetamide afforded 3 and 4 instead of the expected 2A. Compound 5 cyclised into 3‐pyridoquinazolone 6 while its 2‐(4′‐methylpiperazin‐1′‐yl analogue 9 was observed to be unstable for the attempted ring‐opening and reclosure to 42. “From the bottom” cyclisations of 10A‐10C, via intermediary amines 11A‐11C failed and pyridoquinazolinone 13 was isolated (Scheme V). The attempted oxidative cyclisation of the compounds 15 and 18 into 2 and 42, respectively, 13 afforded imidazolo[5,4‐b]pyridine derivative (18–19), while 15 remained unchanged. 3‐Acylamino‐2‐arylaminopyridines (21‐24), cyclised into imidazolopyridines 29‐30. Model compounds 45‐50 were prepared to study selective aminolysis of the chlorine atoms in 2‐chloro‐3‐(2′‐chlorobenzoyl)aminopyridine 1, and its N‐oxide 35.

5,11‐Dihydro‐6H‐pyrido[2,3‐6][1,4]benzodiazepin‐6‐one (1), a basic intermediate in the preparation of 11‐α‐aminoacetyl derivatives with important biological activities, has been obtained by a three‐step synthesis starting from easily available isatoic anhydride and anhydro ornithine. Some model cyclisation reactions leading to 5‐member ring derivatives 10 and 12 instead of 7‐member ring analogues of 1, are reported. Easy transformations of the tetrahydro congener of 1, i.e., compound 4 into 19, which actually represents a tetrahedral intermediate in the transformation of 5 into 4, is noticed. Further rearrangement of 19 into spiro compound 20, and return of the latter into 5 is described.

Bei der Behandlung mit Hydroxylamin/Alkali erhält man aus den Nitro‐ imidazol‐carbonsäuren (IIa)‐(IIc) die Amino‐Verbindungen (IIIa)‐(IIIc), die durch Polyphosphorsäure (PPA) zu den Lactamen (IV) cyclisiert ′werden i können.