Where Synthons Provide Nl

Since Nl and N4 are always provided by ammonia or an amine, examples in this small but significant category are classified according to the nature of the C—C synthons (which are identical in all examples reported recently). 

Bis(benzofuran-2-yl)glyoxal (304) and ammonium chloride gave 2,3,5,6-tetrakis(benzofuran-2-yl)pyrazine (305) (MeOH, sealed, 210°C, 2 h %).546 

4-Hydroxy-3-hexanone (propionoin 306, R = Et)and ammonium acetate gave 2,3,5,6-tetraethylpyrazine (307, R = Et) (neat, reflux, 16 h 50% presumably an aerial oxidation was involved) 1000 4-hydroxy-2,5-dimethyl-3-hexanone (306, R = Pr ) likewise gave 2,3,5,6-tetraisopropylpyrazine (307, R = IV) (44%).1000 

Benzoin (306, R = Ph) and ammonium acetate gave 2,3,5,6-tetraphenylpyrazine (307, R = Ph) (neat, 120°C, 24 h 30% after separation from a byproduct) 1120, cf 934 2,3,5,6-tetrakis (2,2 -bipyridin-6-yl)pyrazine (30%) was made somewhat similarly and its structure was confirmed by X-ray analysis.540 

Note The formation of alkyl- and hydroxyalkylpyrazines from glucose or glyc-eraldehyde and ammonium hydroxide at 150°C has been studied.1425 

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