Heterocycles pyrazines

Figure C3.3.5 shows typical data obtained from experimental studies of tlie type described above, where tlie hot donor is tlie nitrogen heterocycle pyrazine, C Fl N, initially excited by an excinier laser to an energy of 40 640...

Lindsley and coworkers prepared functionalized quinoxalines and heterocyclic pyrazines in excellent yields from 1,2-diketone intermediates under the action of microwave irradiation (Scheme 10.50) [104]. In addition to being a general method for synthesis of a variety of aryl/heteroaryl 1,2-diamines and 1,2-diketones, this procedure suppresses the formation of the polymeric species characteristic of traditional thermal conditions. 

Examination of the pyrazino[2,3-rf]pyrimidine structure of pteridines reveals two principal pathways for the synthesis of this ring system, namely fusion of a pyrazine ring to a pyrimidine derivative, and annelation of a pyrimidine ring to a suitably substituted pyrazine derivative (equation 76). Since pyrimidines are more easily accessible the former pathway is of major importance. Less important methods include degradations of more complex substances and ring transformations of structurally related bicyclic nitrogen heterocycles. 

R] Simpson, ]. C. E. Cinnolines. In The Chemistry of Heterocyclic Compounds. Condensed Pyridazine and Pyrazine rings (Cinnolines, Phthalazines, and Quinoxalines)-, Weissberger, A. Ed. Interscience Publishers New York-London, 1953 p3. 

Synthetic studies on biological activities of marine-origin polycyclic bis-steroid systems with 0-heterocyclic and pyrazine fragments or spirooxazoline fragment 99PAC1095. 

Chemistry of conjugated heterocycles built from pyridazine or pyrazine ring fused with bicyclic (norbomadiene, bomene, or azanorbomene) skeletons 98YGK192. 

Armand and coworkers have shown that, while 1,4-dihydropyrazines are the initial products of the electrochemical reduction of pyrazines, they could not be isolated and readily isomerize in solution into 1,2- or 1,6-dihydropyrazines depending on the substitution pattern in the heterocyclic ring (74CJC3971 84MI1). The rate of the isomerization depends on the type of pyrazine as well as the pH and the nature and amount of the cosolvent. 

Hydroxy group of 8-hyd oxy-2-cycloalkyl-2,3,4,6,ll,lla-hexahydro-l//-pyrazino[l,2-i]isoquinoline-l,4-diones was alkylated with allyl bromide, 2-(bromodifluoromethyl)pyridines, l-(bromodifluoromethyl)- and l-(bro-momethyl)benzenes, halomethyl derivatives of different heterocycles (pyridine, pyrazine, pyrazole, pyrrole, thiazole, thiophene) in the presence of CS2CO3 or K2CO3 (98MIP7). Hydroxy group of 8-hydroxy-2-cyclopentyl-... 

McWeeny, R., Proc. Phys. Soc. A70, 593, (i) Electronic absorption spectra of heterocyclic systems. I. A comparison of theoretical methods pyridine and pyrazine. ... 

Microwave and fluorous technologies have been combined in the solution phase parallel synthesis of 3-aminoimidazo[l,2-a]pyridines and -pyrazines [63]. The three-component condensation of a perfluorooctane-sulfonyl (Rfs = CgFiy) substituted benzaldehyde by microwave irradiation in a single-mode instrument at 150 °C for 10 min in CH2CI2 - MeOH in the presence of Sc(OTf)3 gave the imidazo-annulated heterocycles that could be purified by fluorous solid phase extraction (Scheme 9). Subsequent Pd-catalyzed cross-coupling reactions of the fluorous sulfonates with arylboronic acids or thiols gave biaryls or aryl sulfides, respectively, albeit it in relatively low yields. 

Heterocyclic nitrogen donors and their adducts with zinc chloride have been studied.623,624 A large number of other ligand systems have also been characterized, for example, zinc halide adducts of 2,2-dimethylpropane-1,3-diamine and hexamethylphosphoramide have been studied.625,626 The formation of mixed ligand complexes with chloride and substituted pyridines has been studied.627 The zinc tris(pyridyl) chloride anion has also been structurally characterized.628 Manganese(II) ions have been used to probe the stereochemistry in reactions of zinc halides with pyrazine.629... 

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