Oxazolo pyrazine

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... 

The mass spectrum of formycin (54a) showed M+ and MH+ ions due to the protonated base moiety of the molecule <78MI 712-01). The mass spectra of 5-substituted oxazolo[4,5-d]pyrimidines (78) proceeds via loss of the C-5 substituent <82KGS1255>. The main fragmentations of substituted imidazo[4,5-/>]pyrazines (79) <89KGS532> and oxazolo[5,4- have been determined. 

Acyl derivatives of perhydro-l,4-dioxopyrrolo[l,2-a]pyrazines are rapidly hydrolyzed to the 2-unsubstituted compounds under very mild conditions. The 2-pyruvoyl compound 86 loses the N-acyl group on boiling in water or methanol, on treatment with ammonia in methylene chloride, on exposure to dilute sodium hydroxide solution, and on treatment with p-toluidine at 50-60° for 30 sec. Similarly the methoxy-propionyl compound 142 is extremely sensitive to alkali, immediately reacting with 0.1 M sodium hydroxide solution at 0°. This compound is also deacylated by ammonium hydroxide solution in a few minutes or by sodium bicarbonate solution after several hours. This behavior contrasts sharply with that of the isomeric oxazolo compound 143 and helps to justify the tricyclic formulation adopted for such compounds. Hydrolysis of the 3S,8aS isomer of compound 142 is accompanied by rapid inversion... 

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