5-Hydroxy-3,6-dimethyl-2 pyrazinone

A rather different route to hexadentate ligands containing 3-hydroxy-2-p5rridinone units is based on the reaction of an appropriate pyrazinone with dimethyl acetylene dicarboxylate, which replaces one of the ring-nitrogen atoms by carbon (82). 

Iminodipropiononitrile (53) gave 6-hydroxy-3,5-dimethyl-3,4-dihydro-2(l//)-pyrazinone (54) (HCl/EtOH, 0°C, 12 h then Na2C03—H20 18% by a yet unconfirmed mechanism).577 Also other examples 436 747,749,1180,1284... 

Acetoxy-3,6-dibenzyl-5-methoxypyrazine gave 3,6-di benzyl-5-methoxy-2(l//) -pyrazinone (29) (K2C03, MeOH—H20, reflux, 30 min > 95%) 312 2,5-diace-toxy-3,6-dimethylpyrazine gave 5-hydroxy-3,6-dimethyl-2(l//)-pyrazinone (30) (KHC03, MeOH, reflux, 50 min 53%).1386... 

For example, I -bcnzyloxy-2(l //)-pyrazinone (217, R = H) afforded 70% of 1-hydroxy-2( I //)-pyrazinone (218, R = H) [sometimes written as its tautomer, 2-pyrazinol 1-oxide (218a, R = H) on catalytic hydrogenation over palladium-on-charcoal in methanol for 20 min.588 The homologous l-benzyloxy-5,6-dimethyl-2( I //(-pyrazinone (217, R = Me) gave l-hydroxy-5,6-dimethyl-2(l//)-pyrazinone (218, R = Me), either by a similar hydrogenation (76%) or by hydrolysis in acetic acid-hydrogen bromide under reflux for 10 min (81%, as hydrobromide).588 1085... 

Benzyloxy-5,6-diphenyl-2(l//)-pyrazinone 5- Benzyloxy-1 -hydroxy 3,6-dimethyl-... 

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