From a Pyrazine Substrate with or without Synthon s

FROM A PYRAZINE SUBSTRATE WITH OR WITHOUT SYNTHON(S) 

This potentially wide category of primary syntheses remains almost unutilized apart from the few examples here given. 

2-Ethoxycarbonylmethyl-3-(2-formylethyl)pyrazine (334) (freshly liberated from its acetal) gave a separable mixture of ethyl 6-hydroxy-5,6,7,8-tetrahydro-5-quinoxalinecarboxylate (335) its dehydration product, ethyl 7,8-dihydro-5-quinoxalinecarboxylate (336, R = Et), and the hydrolysis product, 7,8-dihy-dro-2-quinoxalinecarboxylic acid (336, R = H) [NaH, Et20, 0°C, 2 h 15%, 37%, and 37%, respectively when the aqueous workup was carried out at 0°C, product 335 predominated].  

5-Bis(triphenylphosphoniomethyl)-2,3-pyrazinedicarbonitrile dibromide (338), prepared from tbe corresponding bis(bromometbyl) intermediate (337), reacted with benzil to afford 6,7-dipbenyl-2,3-quinoxalinedicarbonitrile (339) (NaH, Me2NCHO, 20°C 125°C, 9 b 58%) several analogs were made similarly.  

3-Bis(dibromometbyl)pyrazine (344) and etbynylbenzene gave 6-pbenylqui-noxaline (346), possibly via tbe unisolated intermediate (345) (reactants, Nal, little Me2NCHO, microwave hv, open vessel, 20°C 90°C, 15 min 38%) prop-1-ynylbenzene or 1-etbynylnapbtbalene likewise gave 6-metbyl-7-pbenylquinoxaline (43%) or 6-(napbtbalen-l-yl)quinoxaline (41%), respectively,  

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From a Pyrazine Substrate with or without Synthon(s)... 

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