Protium–deuterium exchange of substituted pyridines in neutral D2O at elevated temperatures

H–D exchange of a series of pyridines 1–15, 10H-pyridino[3,2-b][1,4]benzothiazine (16), phenothiazine (17), and aniline has been carried out in neutral D2O at elevated temperatures. The substrates undergo selective exchange and are generally isolated in good yield. Cyanopyridines 4,5, and 6 hydrolyze readily in D2O at elevated temperatures, and the resultant carboxylic acids decarboxylate. This reaction provides a convenient one-step route to selectively labelled pyridines. Possible mechanisms of exchange are presented.