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A Pd-catalyzed regioselective H/D exchange at the α-position of pyridines was achieved by employing secondary phosphine oxide as an internal base. The proposed five-membered structure enabled the reaction to overcome its conventional ortho-directing feature, allowing the efficient deuteration of pyridines and quinolines at adjacent sites of N-atoms. [ABSTRACT FROM AUTHOR]

A ligand-free, palladium-catalyzed ortho -deuteration of aromatic carboxylic acids was developed using D2 O as the deuterium source. Compared to their meta -substituted analogues, an unusually lower reactivity in para - and ortho -substituted benzoic acids toward hydrogen isotope exchange was observed. Further investigation revealed that the reaction temperature is a critical parameter for the reactivity, and the modified conditions can afford deuterated products with good to excellent deuterium incorporation. [ABSTRACT FROM AUTHOR]

A regioselective deuteration at the β- and γ-position of pyridines is reported. Efficient deuteration occurred with a combination of KOtBu and DMSO-d6, replenishing the prevailing α-deuteration of the pyridine systems. Preliminary mechanistic studies suggested that the dimsyl carbanion acts as one of the key intermediates. [ABSTRACT FROM AUTHOR]