Transition-metal-free C–N and C–C formation: synthesis of benzo[4,5]imidazo[1,2-a]pyridines and 2-pyridones from ynones

Abstract

We have developed a facile method for the synthesis of benzo[4,5]imidazo[1,2-a]pyridines and 2-pyridones from readily available ynones and 2-methylbenzimidazoles or acetamides.

Simple inorganic base promoted polycyclic construction using mucohalic acid as a C3 synthon: synthesis and AIE probe application of benzo[4,5]imidazo[1,2-a]pyridines

“…Based on the abovementioned experimental results and the related literature, 17,18,26,37 a plausible reaction mechanistic pathway is proposed in Scheme 4. Initially, under the action of a base, the nucleophilic substitution reaction of 2 with muco-bromic acid 1a generates intermediate A .…”

“…Initially, under the action of a base, the nucleophilic substitution reaction of 2 with muco-bromic acid 1a generates intermediate A . 17 Secondly, decarboxylation takes place to give B . 26 Then, intermediate B can react with another NH-containing heterocyclic nucleophile ( 2 or 3 ) to give the intermediate C by Michael addition, and C undergoes a base-promoted dehydrohalogenation reaction to give intermediate D ( e.g.…”

“…Lei 15 and Chen 16 reported the electrochemical oxidative annulation of N -phenylpyridin-2-amine as another green method (Scheme 1b). An inorganic base promoted intermolecular tandem Michael addition/cyclization using ynones (Scheme 1c) 17 or 2-bromocinnamaldehyde (Scheme 1d) 18 also can be an efficient strategy. 17,18 Although the abovementioned methods are useful for constructing benzo[4,5]imidazo[1,2- a ]pyridines, it is also meaningful to develop other effective and practical routes ( e.g.…”

“…An inorganic base promoted intermolecular tandem Michael addition/cyclization using ynones (Scheme 1c) 17 or 2-bromocinnamaldehyde (Scheme 1d) 18 also can be an efficient strategy. 17,18 Although the abovementioned methods are useful for constructing benzo[4,5]imidazo[1,2- a ]pyridines, it is also meaningful to develop other effective and practical routes ( e.g. , multicomponent reactions with step economy 19 ) for the green synthesis of this valuable chemical structure with multiple functions.…”

A Practical Synthesis of 1‐Azine‐pyridin‐2(1H)‐ones from Azine N‐oxides and Pyridin‐2(1H)‐ones under Mild Reaction Conditions

“…Through transition‐metal‐catalyzed cyclization reaction of N ‐aryl‐2‐aminopyridines with benzyl acrylate, Li et al reported a Rh(III)‐catalyzed oxidative coupling reaction to produce the corresponding products in the presence of Cu(OAc) 2 in DMF at 100 °C for 12 h (Scheme 1b) [9] . Following that, a number of methods for the same purpose were developed through the cyclization reaction of N ‐aryl‐2‐aminopyridine with alkynes, [10] 2‐aminopyridine with acetaldehydes [11] or N ‐acetyl‐2‐aminopyridine with ynones [12] . However, the use of transition‐metal complexes, relatively inconvenient reaction conditions and uncommonly used starting materials greatly limited the application of these strategies.…”