Comparative Study on the Reactivity of 6‐Haloimidazo[1,2‐ a ]pyridine Derivatives towards Negishi‐ and Stille ‐Coupling Reactions

The scope of the Suzuki ‐cross‐coupling reaction of 6‐haloimidazo[1,2‐ a ]pyridines is dependent on the availability of the (hetero)arylboronic acids. Thus, with the aim to develop expanded applications of (hetero)arylations of imidazo[1,2‐ a ]pyridines, we investigated the Negishi ‐ and Stille ‐cross‐coupling reactions at the 6‐position. Remarkably, attempts to apply the Negishi ‐cross‐coupling conditions to the organozinc derivative prepared from 6‐haloimidazo[1,2‐ a ]pyridine via a lithiumzinc exchange led to the 5‐phenyl compound 3 in 54% yield instead of the desired 6‐phenyl isomer ( Scheme 1 ). In contrast, various commercially available halogenated five‐ or six‐membered‐ring heterocycles were efficiently coupled to the 6‐(trialkylstannyl)imidazo[1,2‐ a ]pyridine under Stille conditions ( Table 2 ).