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2‐Aminopyridines as an α‐Bromination Shuttle in a Transition Metal‐Free One‐Pot Synthesis of Imidazo[1,2‐a]pyridines
Authors:Irwan Iskandar Roslan  Kian‐Hong Ng  Gaik‐Khuan Chuah  Stephan Jaenicke
Abstract:A wide range of imidazo[1,2‐a]pyridines are accessible from cheap and readily available 2‐aminopyridines and 1,3‐dicarbonyl compounds using a unique CBrCl3/2‐aminopyridine system for bromination at the α‐carbon. 2‐Aminopyridine is not only the substrate but also acts as a bromination shuttle, transferring the bromine atom from CBrCl3 to the α‐carbon of the 1,3‐dicarbonyl. The reaction mechanism involves a series of reversible steps, including an addition reaction with cyclic transition state, to form a bromo‐hemiaminal intermediate. Isolated yields of up to 97% were obtained under mild conditions and at short reaction times in this transition metal‐free, one‐pot synthesis.
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Keywords:bromination  C?H activation  C?N bond formation  cyclization  fused ring systems
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