Pyrazine synthesis

An alternative approach to the use of a-aminoketones involves acetals (72JOC221) and pyrazine-2,3-diones have been synthesized by this route (Scheme 58). The acetals are readily available from the phthalimido derivatives via the a-chloroketones. Hemiacetals have also served as a starting point for pyrazine synthesis, although in most cases hemiacetals are too labile to be easily prepared examples are common in the 2-amino-2-deoxy sugar series 2-amino-2-deoxy-D-glucose for example dimerizes to the pyrazine (101) when generated in situ from the hydrochloride salt (68JAP6813469). 

Furo[3,4-d]oxazoline, cis-tetrahydro-2-phenyl-synthesis, 6, 1017 Furopyrans, 4, 993-995 Furopyrazines, 4, 988 Furo[2,3-6]pyrazines synthesis, 4, 988... 

Imidazolidine, 4,5-dichloro-l,3-diacetyl-imidazo[4,5-6]pyrazine synthesis from, 5, 646 Imidazolidine, 1,3-dimethyl-conformation, 5, 355 Imidazolidine, diphenyl-dehydrogenation, 5, 427 Imidazolidine, 2-imino-1-substituted nitration, 5, 427... 

Oxazolo[4,3-c][l,4]oxazine, perhydro-conformation, 6, 662 Oxazolo[2,3-h]oxazoles synthesis, 6, 989 Oxazolophanes synthesis, 7, 774 (3,5)Oxazolophanes synthesis, 7, 770 5ff-Oxazolo[3,2-a]pyrazine synthesis, 6, 664 5f/-Oxazolo[3,2-6]pyridazine synthesis... 

H,3H- Pyrrolo[l, 2-c]oxazole-l, 3-dione, 5,6,7,8-tetrahydro-IR spectra, 6, 978 [2.2](2,5)Pyrrolophane, N-aryl-rearrangements, 4, 209 Pyrrolophanes natural products, 7, 764 synthesis, 7, 771 Pyrrolophanes, N-aryl-synthesis, 7, 774 (2,4)Pyrrolophanes synthesis, 7, 771 Pyrrolo[3,4-c]pyran-4-ones synthesis, 4, 288 Pyrrolopyrans synthesis, 4, 525, 526 Pyrrolopyrazines synthesis, 4, 526 Pyrrolo[l, 2-a]pyrazines synthesis, 4, 516 Pyrrolo[2,3-6]pyrazines Mannich reaction, 4, 504 Vilsmeier reaction, 4, 505 Pyrrolo[3,4-c]pyrazole, 1,3a,6,6a-tetrahydro-structure, 6, 976 synthesis, 6, 1019 Pyrrolopyrazoles synthesis, 5, 164 Pyrrolo[l,2-6]pyrazoles synthesis, 6, 1002, 1006 Pyrrolo[3,4-c]pyrazoles reactions, 6, 1034 synthesis, 6, 989, 1043 Pyrrolo[3,4-c]pyrazolones synthesis, 6, 989 Pyrfolopyridazines synthesis, 4, 517 Pyrrolo[l, 2-6]pyridazines synthesis, 4, 297 6/7-Pyrrolo[2,3-d]pyridazines synthesis, 4, 291 2/f-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291 6/7-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291... 

G A S T A L 0 I Pyrazine Synthesis Pyrazme synthesis from a-oximmokeiones via a-aminoketones... 

Pyrantel, 303 Pyrazine synthesis, 298 Pyridazine synthesis, 304 Pyrimidine synthesis, 302, 467... 

Ring closure y to a heteroatom is also a rather uncommon [5 + 1] procedure although there are some important exceptions. The most widely investigated is the Bernthsen acridine synthesis in which a diarylamine is condensed with a carboxylic acid in the presence of a Lewis acid (equation 73). More recently, it has been shown that acylanilines react with the Vilsmeier-Haack reagent to give quinolines in good yield (e.g. equation 74) and the mechanism of the reaction has been elucidated. A final example of [5 +1] ring closure y to a heteroatom which is of occasional use is the pyrazine synthesis outlined in equation (75). 

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