Pyridine pyrimidine-6-ones

Pyrazolo[3,4-b]pyridin-4-one, 1,3,6-trimetbyl- C NMR, 5, 332 <75JHC517) Pyrazolo[3,4-b]pyridin-6-one, 1,3,4-trimetbyl- C NMR, 5, 332 <75JHC517) Pyrazolo[l,5-a]pyrimidine electron density, 5, 306 <75CJC119) Pyrazolo[3,4-d]pyrimidine electron density, 5, 306 <58JCS2973, 69CJC1129) Pyrazolo[3,4-d]pyrimidine, 4-amino- C NMR, 5, 310 <58JCS2973) Pyrazolo[4,3- /]pyrimidine electron density, 5, 306 <58JCS2973)... 

First we consider diacetylene transformations leading to fundamental heterocycles (pyrroles, thiophene, selenophene, tellurophenes, pyrazoles, isoxazoles, pyridines, pyrimidines). Then cyclization reactions involving 1-heterobut-l-en-3-ynes, 4-heterobut-3-en-2-ones, and 4-heterobut-3-yn-2-ones (91UK103 92KGS867 00UK642) as diacetylene equivalents are discussed. 

Spickett and Wright investigated the reactions of 4-substituted 3-amino-1,2,4-triazoles and EMME in acetic acid for 24-48 hr [67JCS(C)503]. Generally, they obtained [l,2,4]triazolo[l,5-a]pyrimidine-7-ones (1124) in 38-56% yields. In the case of the benzyl derivative (R = CH2Ph), the isomeric triazolo[l, 5-a]pyrimidin-5-one (1125) was also isolated from the mother liquor, in 5% yield. From the 4-ethyl and 4-phenethyl derivatives (R = Et, CH2CH2Ph), l-(l,2,4-triazol-3-yl)pyridin-2-ones (1126) were also obtained in 1-2% yields. 

Pyrimidin-2-one exchanges its 5-hydrogen much faster than pyridin-2-one. However, this is due to the existence of a small proportion of the covalent hydrate (106) which undergoes rapid exchange. 

The negative charge in a Meisenheimer complex, can be stabilized not only by a nitro substituent at one of the charged atoms, but also by a ring nitrogen. Therefore, pyridines, pyrimidines, and 1,3,5-triazines containing a Cl atom in the 2-, 4-, and/or 6-position, likewise enter into Ar-SN reactions via Meisenheimer complexes very readily. 

Ring opening of 3-(phenylsulfonyloxy)pyrido[3,4-d]pyrimidine-2,4-dione (587) with sodium methoxide, followed by a Lossen rearrangement gave the hydrazinopyridine ester (588) which in refluxing acid yielded 1 //-pyrazolo[3,4-c]pyridin-3-one (589) (Scheme 75) <74JHC163>. 

Using the general method described in Section 7.08.10.2 <74JHC163> 3-(phenylsulfonyloxy) pyrido[4,3-fi ]pyrimidine-2,4-dione (590) ring opens with sodium methoxide and rearranges to a hydrazinopyridine ester, which in refluxing acid yields l//-pyrazolo[4,3-c]pyridin-3-one (591) (Equation (59)). 

Other diimine ligands are shown in (104-106) with systems containing one pyridine and one other heterocyclic mono-aza ligand, and the C atoms of the py ring can be replaced by one or more N atoms to give, for example, (107). Other coupled sets are pyrazole plus pyrazole (108), pyrazole plus imidazole (109), and imidazole plus imidazole (110) together with coupled pyrazines (111), pyrimidines (112), (113), and pyridazines (114). 

C-Hydroxy-8-azapurines do not exist as such but as equilibrium mixtures (e.g., 8 9) in which the cyclic amide tautomers greatly preponderate over the hydroxy tautomer. This behavior parallels what was found in the pyridine, pyrimidine, and purine series on evidence from ionization constants and the UV spectra of C- and A -methyl derivatives. A formal name for9 is 1,6-dihydro-8-azapurin-6-one but such specification of the hydrogen atom s position is, in the absence of data, risky for example, pyrimidin-4-one is an equilibrium mixture in which tautomers with mobile hydrogen on N-3 and N-1 preponderate in a 5 2 ratio, respectively. Hence the simpler names, such as 8-azapurin-6-one, will be used in this review. 

A series of dopamine D3-receptor antagonists was pre-pared. Changing from the l//-pyrimidin-2-one (X = N) compound (53) to the l//-pyridin-2-one (X = CH) analog (54) increased the logP value 1.1 units and decreased PSA by 13 angstroms, which resulted in greater brain penetration and a B/P ratio of 3.7. 

Pyridine Pyridine 1-Oxide Pyridin-2-one Pyrimidine Pyran-2-onc... 

Imidazol 1,2-0Ipyridine, 879, 13.39 Imidazol I..5-a pyridine, 874. 13.39 Imidazol 1,5-a Ipyridine, 1.321 lmidazo 4,5-6jpyridine, 741 Imidazol 1,2-a ipyridin-3-one. 1000 Imidazol 1,2-a pyridin-5-one. 917 Imidazol 1,2-ajpyridin-7-one. 918 Imidazo 4,5-6 pyridin-2-one. 1129 Imidazo 4.5-b)pyridin-2-one, 948 Imidazo 4,5-( pyridin-2-one, 1139 Imidazol 1,2-a]pyrimidine, 874 Imidazoll,2-( pyrimidine, 998, 1237 Imidazol 1,2-a pyrimidin-4-one, 1009 Imidazol 1,2-a pyrimidin-5-one, 1300 Imidazoj 1,2-a jpyrimidin-7-one, 1300 Imidazol 1.2-ajpyridin-7-one. 1106 Imidazoll,2-r quinazolin-5-one, 886 lmidazo 4,5-/ quina/olin-7-one, 684 lmidazo 4.5-/> quinazoiin-8-one, 1161 Imidazol 1,5-a Iquinoiine, 998 Imidazoj4.5-( quinoline, 1313 Imidazo 4..5-/Iquinoiine, 981. 989 Imidazo 4,5-/ quinolin-7-one. 684 Imidazol 1,2-a Iquinoxaline, 975 Imidazol 1.5.4-de quinoxaline, 776 Imidazol I 3,4-de quinoxaline-2.5-dione, 1000... 

Oxazolo[5,4-6]pyridine, 704, 906 Oxazolo[3,2-a]pyridin-5-one, 918 Oxazoio[4,5-6]pyridin-2-one, 716, 1226 Oxazoio[4,5 [Pg.774]

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