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Background: Atropisomers are very interesting stereoisomers having axial chirality resulting from restricted rotation around single bonds and are found in various classes of compounds. ortho- Substituted arylpyridines are an important group of them. A regio- and atropselective Suzuki-Miyaura cross-coupling reaction on 3,4,5-tribromo-2,6-dimethylpyridine was studied. Results: Reactions with various amounts of ortho -substituted phenylboronic acids with 3,4,5-tribromo-2,6-dimethylpyridine gave a series of mono- di- and triarylpyridine derivatives which allowed to draw conclusions about the order of substitution. Also, the observed selectivity in the case of ortho -methoxyphenylboronic acid suggested an additional metal O -chelation effect in the transition state, apparently not present in the ortho -chloro analogues. The rotational barrier in selected atropisomers was determined on the basis of HT NMR and thermal epimerisation experiments. The structure of most presented atropisomeric derivatives of 2,6-dimethylpyridine was confirmed by single-crystal X-ray analysis. Racemic chiral, differently substituted atropisomers were also examined by 1 H NMR spectroscopy in the presence of a chiral solvating agent. Conclusion: This regio- and atropselectivity may be generally applicable to other arylpyridine systems. A regio- and atropselective Suzuki-Miyaura cross-coupling process has been observed, giving an efficient access to a class of atropisomeric compounds. An opposite selectivity using a differently ortho -substituted phenylbornic acid was observed.

beilstein journal of organic chemistry

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected <i>ortho</i>-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine