Pyrazines, literature reviews

Isolated and benzo-fused diazine rings are key structural elements in many natural and synthetic compounds of current, active interest. This contribution relates highlights from many of the studies on the diazines pyridazine, pyrimidine, pyrazine, and their benzo-fused derivatives cinnoline, phthalazine, quinazoline, quinoxaline, and phenazine published in English in the journal literature during 1995, as covered by Chem. Abstr. through volume 124, issue 9. Review articles published in 1994 and not cited in Prog. Heterocycl. Chem. have been included. 

The furoxanopyridine (584) has its azole ring expanded into a pyrazine when reacted with enamines. The reactive species is assumed to be the 2,3-dinitrosopyridine (585) (80M407). Recent review literature on benzofuroxanes suggests extension of the enamine reaction to enolate anions and related species (75S415,76H(4)767). 

The primary synthesis of pyrazines from other heterocyclic systems has a body of literature that is quite modest by comparison with those for pyridazines1687 and pyrimidines.1688 Earlier information on such syntheses has been summarized in Barlin s original book1686 and some more recent data have been reviewed thoughtfully from time to time.1677,1689... 

This supplement seeks to build on the solid foundation established by Dr. G. B. Barlin s original volume, The Pyrazines, that appeared within this series in 1982. That original book presented the first comprehensive review of pyrazines, embracing a mass of important historical material as well as a modem systematic treatment of pyrazine chemistry. Not surprisingly, it stimulated a great deal of research in all aspects of the field, resulting in the need for a supplementary volume to cover literature published between 1979 and 2000, inclusive. 

In our view, it is this circumstance which accounts for the chemical and physical similarities between thiophene and benzene, as well as between pyrazine and 1,2,5-thiadiazole, which have frequently been pointed out in this review and in the chemical literature. In a formal sense the sulfur atom having two pd orbitals is like an ethylenic fragment with two p orbitals. We therefore propose that a sulfur-containing heterocycle be termed quasiethylenic with its cyclic counterpart in which the sulfur atom is replaced by two doubly bonded carbon atoms. 

The chemistry of hydropyrazines (including piperazines) has not been treated in the comprehensive manner used for the pyrazines in this volume because it is, strictly speaking, beyond the scope of this work. To provide an entry to the literature, references to reviews of the older literature are summarized in Table XI.1 (35-39, 1524-1534), and a selection of preparations and reactions, drawn from more recent publications are discussed. 

Pratt (36) in 1957 published a comprehensive review which included reduced pyrazines (di- and tetrahydropyrazines, piperazines, and piperazinones), and the literature prior to 1957 is generally not further examined. 

This volume summarizes published pyrazine chemistry with emphasis on syntheses, properties, and reactions of pyrazines and pyrazine iV-oxides (Chapters 1-X). Treatment of theoretical aspects is minimal. Although not strictly relevant. Chapter XI is presented as a summary of earlier reviews and more recent literature of reduced pyrazines (including piperazines). The literature recorded in Beilstein to 1929 and Chemical Abstracts through 1978 (Volume 89) has been covered together with selected references to 1980. Whereas every reasonable effort has been made to incorporate most significant material, no attempt has been made to include all relevant data. Tables have been incorporated in the text to extend the range of examples. 

Much literature has appeared describing ring contractions of pyrimidines, pyrazines, and triazines into imidazoles, and the field has been reviewed. ... 

Only a few new syntheses of the fully unsaturated pyrrolol 1,2-a]-pyrazine system have appeared since the literature was last reviewed.1 Acheson and Foxton5 obtained low yields of the triesters 134 and 135 Eq. (43)1 from the corresponding pyrazines and dimethyl acetylenedi-... 

Pyridazines, pyrimidines, pyrazines and their benzo derivatives continue to be a focal point of many reports. In this contribution, the literature on their chemistry and bio-activity as covered by chemical abstracts vol. 120 and vol. 121 (1994) is reviewed. Owing to space limitations, however, many publications of merit could not be included. 

Classes of chemical compounds having different function groups and odor descriptors, some of which are useful to the flavor or perfume industries were selected for this initial study. For example, alcohols, aldehydes, pyrazines and various benzenoid compounds which have been isolated in the volatiles of cooked meat as reviewed by Hornstein (22) were studied. For each class of chemical compounds literature threshold values obtained only from one laboratory were used in order to prevent errors associated with technique or methodology between laboratories that occur for threshold determinations as discussed by Guadagni al. ) and Powers and Ware (23). 

Abstract This review deals with general and significant developments in the area of chemistry of fluorinated pyrimidine, pyrazine and pyridazine. Diazines bearing fluoro or a-fluoroalkyl substituent at carbon atoms of the heterocyclic ring, as well as their fused derivatives are discussed. The literature data are divided into two parts, which describe synthesis and chemical behavior of ring- and chain-fluorinated diazines (RED and CFD respectively). 

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