Azine -oxides, activating effect

The aza group activation effect in the oxidative amination of azines is less than that of the nitro group. As an illustration the reaction of 4-nitroquinoline and liquid ammonia in the presence of KMn04 produced 3-amino-4-nitroquinoline only in 86% yield [52]. Oxidative amination of 5-nitroquinoline gave 6-amino derivative in... 

The electron-withdrawing effect of typical azines makes chlorine substituents sufficiently reactive that they can participate in palladium-catalysed reactions, even at a pyridine / -position. " a-Activation can serve to allow regioselective reaction in the presence of a /3-halogen (cf. section 2.7.1.1, oxidative addition) and this should be contrasted with lithiation by exchange which shows the opposite regioselectivity. 

Arylation of Thiazoles and Oxazoles. The protocol that was previously developed for the C-H activation of azine and diazine (V-oxides with aryl triflates was used to effect the arylation of flve-membered ring heterocycles, such as oxazoles and thiazoles. In contrast to another protocol that was previously reported by the same group, the transformation did not require an V-oxide function. However, in order to direct the arylation at the C4-position, to prevent the formation of a mixture of regioisomers, and to minimize the generation of diarylated products, a C5-chloride was used as a blocking group. The procedure, which is promoted by palladium acetate and di-tert-butyl(methyl)phosphonium tetrafluoroborate, uses an aryl bromide as the electrophile. 

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