Sonogashira scaffold decoration

Scheme 37 Scaffold decoration via Sonogashira reaction on solid support...

Scheme 6.32 Scaffold decoration of heterocycles using Sonogashira cross-coupling chemistry.

For the further decoration of the pyrazinone scaffold via transition metal-catalyzed chemistry, the Sonogashira reaction [45-50] has also been investigated on the C-3 position of the pyrazinone, applying microwave irradiation conditions (Scheme 17) [29]. It was found that microwave irradiation at 120 °C for 15 min of a mixture of the starting material, Pd(OAc)2, Cul and PPha in TEA/DMF were the appropriate reaction conditions. 

In a recent study, the group of Van der Eycken described the decoration of polymer-bound 2(lH)-pyrazinone scaffolds by performing various transition metal-catalyzed transformations [42]. The readily prepared pyrazinone was specifically decorated at the C3 position by employing microwave-mediated Suzuki, Stille, Sonogashira, and Ullmann protocols (Scheme 7.24), thereby introducing additional diver-... 

The [4+2] cycloaddition reactions of some triazole substituted 3,5-dichloro-2(lH)-pyrazinones have been studied by Kaval et al. (2006). They developed the required intermediates from the corresponding 3,5-dichloropyrazinones, following either a nucleophilic substitution or a Sonogashira reaction to install the alkyne handle on the scaffold. The various triazole derivatives linked to the pyrazinones were synthesized through a microwave-assisted CuAAC reaction. Then [4+2] cycloaddition reactions were carried out under microwave irradiations with dimethyl acetylenedicaiboxylate (DMAD) at 180-200 °C for 10-20 min, and the corresponding highly decorated pyridine and pyridine scaffolds were isolated in good yields. 

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