3- Methoxy-1 -phenyl-2 -pyrazinone

To avoid problems with the separation of regiomers, dimethyl acetylene dicarboxylate (DMAD) was chosen as a dienophile. The intermolecular Diels-Alder reactions were performed in refluxing dichlorobenzene (bp 132 °C), while the intramolecular reaction of alkyne tethered pyrazinone required a solvent with a higher boiling point (bromobenzene, bp 156 °C). In the case of 3-methoxy or 3-phenyl pyrazinones a mixture of pyridinones and pyridines was obtained, while for the alkyne tethered analogue only the di-hydrofuropyridinone was isolated as the single reaction product. 

For the microwave-assisted experiments, both solvents were replaced by 1,2-dichlorobenzene, as it couples very effectively with microwaves (loss-tangent (tan 5) at 20 °C 1,2-dichlorobenzene 0.280 as compared to 0.101 for chlorobenzene). Diels-Alder reactions of 3-methoxy or 3-phenyl pyrazinones with DMAD were performed at a pre-selected maximum temperature of 200 °C, whereas the intramolecular reaction of alkyne tethered pyrazinone required a higher temperature (220 °C). The yields obtained under microwave irradiation are comparable with those obtained under conventional conditions, while for the dihydrofuropyridinone the yield was improved from... 

Hydrolysis. 2-Methoxy-3-methyl-5-phenylpyrazine (16) gave 3-methyl-5-phenyl-2(l//)-pyrazinone (17) (6 M HC1, reflux, 3 h 97%) 1307 other products like 3,6-diisopropyl-2( I //(-pyrazinonc (18, R = Pr ) (97%)1311 and 3,6-diphenyl-2(l/7)-pyrazinone (18, R = Ph) (84%)82 were made similarly. Hydriodic acid may also be used.1307... 

Chloro-3-methoxy-6-methoxymethyl-1 -phenyl-2n //)-pyrazinone 5-Chloro-6-methoxy methyl-1,3-diphenyl-20 //)-pyrazinone 2-Chloro-6-methoxy-3-methyl-5-phenylpyrazine 2-Chloro-6-methoxy-5-methyl-3-phenylpyrazine 5-Chloro-3-methoxy-6-methyl-l-phenyl-2( 1 //t-pvTa/ini iie... 

Chloro-5-methoxy-6-phenylpyrazine 5-Chloro-3-methoxy-l-phenyl-2(17/)-pyrazinone... 

Methoxy-1 -methy l-2( 1/7)-pyrazinono 6-Methoxy-l-methyl-2(l/7)-pyrazinone 5-Methoxy-3-methylthio-2-pyrazinamine 3-Methoxy-1 -phenyl-6-(prop-2-... 

Methoxy-l-phenyl-2(l//)-pyrazinone 3-Methoxy-5-phenyl-2(l//)-pyrazinone 5-Methoxy-3-phenyl-2(l//)-pyrazinone 5-Methoxy-6-phenyl-2(l/7)-pyrazinone 2- Methoxy-3 -propionylpyrazine... 

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