Enantiopure N-protected α-amino glyoxals 1. Synthesis from α-amino acids and some condensation reactions with amines

Synthesis of aromatic heterocycles

“…383 A similar strategy was used to produce pyrazines and quinoxalines from the ketoaldehydes 265. 384 3,6-Diphenylpyridazine was formed as the major product (61%) when the phosphorane 266 was heated in benzene; other pyridazines were also prepared by this reaction. 385 The hydrazones 267 gave 3,6-diaryl-4,5-bis(trifluoromethyl)pyridazines when heated in TFA.…”

Six‐Membered Heterocycles: 1,2‐, 1,3‐, and 1,4‐Diazines and Related Systems

“…Ammonolysis and aromatization give the pyrimidone product. Isoxazolidin-5-one can be obtained as McKervey and coworkers [125] have used N-protected a-amino glyoxals from diazoketones 101, as 1,2-dicarbonyl components, to condense with simple 1,2diamines to form dihydropyrazines (Scheme 19.97). These adducts can be dehydrogenated to pyrazines 102 by treatment with manganese dioxide in the presence of potassium hydroxide.…”

Preparation of quinoxalines, dihydropyrazines, pyrazines and piperazines using tandem oxidation processes

“…The use of co-oxidants, such as DDQ and CAN, in these reactions resulted in complete degradation of the dihydropyrazines 5. We eventually established that the addition of ~0.4 M KOH in methanol 15 to the refluxing reaction mixture after the formation of dihydropyrazines 5 resulted in production of the corresponding pyrazines 6 (Scheme 3). It should be noted that the addition of methanol alone did not achieve the desired transformation.…”