Pyrimido pyrazol

Another strategy is the conversion of isoxazolo[3,4-d]pyridazin-7(6//)-ones (63) via pyrazole derivatives (64) into the new pyrazolo[l, 5 l,6]pyrimido[4,5-c/]pyridazin-7(8//)-ones (65) by final ring closure with acetic anhydride (Scheme 12) <86H(24)3143>. 

Pyrazin 3-Amino-2-cyan-5-(2-furyi)-E9b/2, 31 If. (N-Oxid-Red.) lH-Pyrazol 4-Diazo-5-oxo-3-phenyl-4,5-dihydro- X/4, 525/ El4b, 1114 (Amin 4- NaN02) lH-(Pyrimido 5,4-f]indazol) 5(bzw. 9)-Hydroxy- E8b, 849 (Pyrimidin-Ringschl.)... 

The formation of pyridine IV-imines by an add-catalyzed rearrangement of some diazepinones and related compounds has been extensively investigated by Moore and co-workers (Eq. 9).115 The formation of pyridine N-imines from l/f-l,2-diazepines is also known (Eq. 10).68 69,116,117 Diels-Alder reactions of pyrazoles with dimethyl acetylenedicarboxylate, in the presence of BF3, have been reported to give IV-aminopyridinium salts (Eq. II).118 l,4-Dihydropyrido[l,2-a]-as-triazinium salts and their pyrimido derivatives undergo ring contraction in boiling aqueous acid, yielding 1-aminoimidazo[l,2-a]pyridinium and pyrimidinium salts, respectively (Eq. 

Other examples of this type of reaction, giving l,2,3-triazino(4,5-c] quinolines (112) (53JCS1915) and pyrimido[4,5-d]l,2,3-triazines (113) [84JCS(P1)1471], are shown in Schemes 22 and 23, respectively. An alternative mode of cyclization gives a fused pyrazole ring [96JCS(CC)2711]. 

An earlier report that 6-acetyl-7-(2-dimethylaminovinyl)pyrazolo[l,S-a]pyrimidine (97) reacts with hydrazine hydrate in acetic acid to give 6-methylpyrazoIo [S ,T 2,3]pyrimido[S,4-[Pg.260]

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