New synthesis of 11‐acyl‐5,11‐dihydro‐6 H ‐pyrido[2,3‐b][1,4]‐benzodiazepin‐6‐ones and related studies

New synthesis of 11‐acyl‐5,11‐dihydro‐6 H ‐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 .