Pyridine 1-oxides hydrogen exchange

Fig. 2.9. Experimental hydrogen exchange rate profile for deuteriation of 3,5-dimethyl-pyridine 1-oxide at positions 2 and 4.

Imtdazo[4,5-c]pyridtne, 4,5,6,7-tetrahydro-synthesis, 5, 623, 640, 641 Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-synthesis, 5, 623, 641 Imidazopyridines as anthelmintic, 1, 202 synthesis, 5, 462 Imidazo[l,2-n]pyridines deuterium exchange, 5, 611 diazo coupling, 5, 614 Dimroth rearrangement, 5, 613 halogenation, 5, 611 hydrogenation, 5, 614 Mannich reaction, 5, 612 nitration, 5, 612 1-oxides... 

Pyridine, 3-(dimethylamino)-amination, 2, 236 methylation, 2, 342 nitration, 2, 192 iV-oxide synthesis, 2, 342 Pyridine, 4-(dimethylamino)-in acylation, 2, 180 alkyl derivatives pK, 2, 171 amination, 2, 234 Arrhenius parameters, 2, 172 as base catalysts, 1, 475 hydrogen-deuterium exchange, 2, 286 ionization constants, 2, 172 methylation, 2, 342 nitration, 2, 192 iV-oxide synthesis, 2, 342... 

Treatment of pyridine with NaOD/D20 at elevated temperatures results in eventual replacement of all hydrogen atoms by deuterium. This process presumably involves deprotonation followed by rapid deuteration of the intermediate negatively charged species (cf. equation 21) in a sequential manner. Azine N- oxides are deuterated in a similar way, positions adjacent to the N- oxide exchanging particularly rapidly. Controlled deprotonation of ring carbon atoms a and y to the heteroatom can be accomplished by the use of strong, non-nucleophilic bases and the intermediate carbanions may be trapped by electrophiles (equation 27). The yields in these reactions are in most cases only moderate, however. As expected, deprotonation occurs more easily if the heteroatom is positively charged. 

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