Deprotonation at nitrogen

The reaction of the pyrrole and indole anions with electrophiles are discussed in Section 3.3.1.3.1. 

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In addition to the complexation by the parent, the sulfide radical cation can undergo a deprotonation at a neighboring carbon [cf. reaction (51)]. Also, in the case of thiourea, deprotonation at nitrogen in basic solution competes with a complexation by the parent (Wang et al. 1999). This reaction is, of course, not given by its jV,jV,jV, N -(etramethyl derivative. 

In basic solution, Ura and Thy undergo a series of reactions as depicted in reactions (72)—(76) for Ura as an example (Fujita and Steenken 1981). Ura dissociates athighpH [equilibrium (72) for pfCa values see Table 10.11], Its OH-adductscan also be deprotonated at nitrogen leading to an oxidizing heteroatom-centered radical [reaction (76)]. 

The OH-adduct radicals can become deprotonated at nitrogen. As a consequence of this, water is eliminated from the adduct. This reaction results in the formation of a heteroatom-centered, oxidizing radical e.g. reaction (11)] this may also be formed directly from the deprotonated nucleobase at higher pH [reaction (10)]. At high pH, this radical can undergo a second deprotonation [reaction (12)]. However, this radical anion is not the thermodynamically favoured species under these conditions, and is subsequently reprotonated at carbon (i.e. the heteroatom-protonated acid has a lower p a value than its carbon-protonated isomer) [reaction (14)]. The hydroxyl group can also be eliminated by acid catalysis, which gives rise to a radical cation. These reactions will be discussed below in a separate section. 

In Summary Treatment of primary and secondary amides with base leads to deprotonation at nitrogen, giving amidate ions. Bases abstract protons from the a-carbon of tertiary amides. In the Hofmann rearrangement, primary amides react with halogens in base to furnish amines with one fewer carbon. In the conrse of this process an alkyl shift takes place, which converts an acyl nitrene into an isocyanate. 

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