6
1 Introduction
Figure 7: Formation of a keteniminium ion and stabilisation by a pyridine base. R
4
= H,
CH3, F, Cl, Br or I.
The afore mentioned nucleophilicity of amides enables their selective activation by triflic anhydride even in the presence of aldehydes, ketones, esters and
nitriles. Many reactions have been developed using this method.
[22]
Notably, Maulide et al. discovered that aryl sulfoxides and aryl hydroxamic acids add to the
keteniminium intermediate to trigger a [3,3]-sigmatropic rearrangement event, ultimately yielding -arylated amide products (Figure 8).
[23,24]
Figure 8: Chemoselective -arylation of amides.
The chemoselective -amination of amides can be achieved by the analogous
addition of alkyl azides.
[25]
The unusual enamine intermediate II cyclises to a
2H-azirinium, the hydrolysis of which reveals the final products (Figure 9).
Figure 9: Chemoselective -amination of amides.