Of heterocyclic rings

The shapes of heterocyclic rings are very much like those of their all carbon analogs Thus six membered heterocycles such as piperidine exist m a chair conforma tion analogous to cyclohexane... 

Fluorine and phosphorus occasionally appear attached to, or as part of, heterocyclic rings. However, very little systematic attention has been paid to them, in the area of the azines,... 

STRUCTURE OF HETEROCYCLIC RINGS WITH MORE THAN SIX RING ATOMS... 

Vapor phase pyrolysis of 2-dimethylaminoazirine (168), on the other hand, proceeds in a similar manner at 340 °C to give substituted azadiene (169) in high yield (7SJA4409). Azadiene (169) has been employed in the construction of heterocyclic rings such as pyridines via a [4-1-2] cycloaddition-elimination sequence. 

The naming of heterocyclic ring carbonyl compounds always seems to present difficulties the following account of the procedures used may provide some clarification. 

The aldehyde functionality present in 3-phenyl-2H-azirine-2-carbox-aldehyde reacts selectively with amines and with Qrignard and Wittig reagents to give a variety of substituted azirines. These azirines have been used, in turn, to prepare a wide assortment of heterocyclic rings such as oxazoles, imidazoles, pyrazoles, pyrroles, and benzazepins. ... 

There are several instances of heterocyclic ring annellation, including 4,5-furoxano and 4,5-furazano ring fusion (17 and 18),... 

Replacement of heterocyclic rings in nucleosides by ring systems which do not occur in nature represents another approach to compounds which may have activity against viral and neoplastic diseases. One of the early successes in this category involves replacement of a pyrimidine ring by a triazine. The synthesis starts with a now classical glycosidation of a heterocycle as its silylated derivative (146) with a protected halosugar (145), in this case a derivative of arabinose... 

Synthesis by Formation of Heterocyclic Ring Main Features... 

The synthesis of heterocyclic compounds using transition metals and using heterocyclic compounds as intermediates in the synthesis of other organic compounds will bean additional feature of each volume. Pathways involving the destruction of heterocyclic rings will also be dealt with so that the synthesis of specifically functionalized non-heterocyclic molecules can be designed. Each volume in this series will provide an overall picture of heterocyclic compounds... 

The selection of appropriate polymeric bromine reagent according to the polymeric structure (step of crosslinking, porosity, step of dilution with styrene, granulation, type of heterocyclic ring incorporated, numbers of N) is very important. From production point of view the use of polymeric reagents reduces the costs for solvents and working hours. 

Expansion of heterocyclic rings upon treatment with carbenes... 

An analysis of the principal methods for construction of compounds with 1,2,5-oxadiazole heterocyclic units was published in CHEC(1984) and CHEC-II(1996) < 1984CHEC(6)393, 1996CHEC-II(4)229>. In this chapter only reactions that lead to the formation of 1,2,5-oxadiazole cyclic fragments are considered. The functionalization or replacement of substituents of heterocyclic ring as well as oxidation or deoxidation of nitrogen atoms are described in Section 5.05.4. 

Cyclopentenylacetic acid when treated with sulfur monochloride, Hiinig s base and N-chlorosuccinimide in tetrahydrofuran gave trichlorocyclopenta[l,2]-dithiole ester 104, a product of heterocyclic ring formation, chlorination and dehydrochlorination and, unexpectedly, the conversion of the acid in THF into its 4-chlorobutyl ester (1999JCS(P1)1023 Scheme 52). 

The higher seniority of heterocyclic rings over carbocyclic rings (rule 3) and the higher seniority with higher unsaturation for cyclic subunits (rule 7a) yield the CRU XV with the name poly(pyridine-2,4-diyl-1,4-phenylenecyclohexane-1,4-diy 1). 

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