Heterocyclic bridgehead nitrogen

The infrared (IR) spectra of these compounds were mostly studied in the solid state which showed all the basic peaks characteristic of various functionalities attached to such bicyclic heterocycles with bridgehead nitrogen atoms. The difference in the frequency of carbonyl and carbon nitrogen double bond in tautomers of compound 18 (R = H) has been discussed previously in CHEC-II(1996) <1996CHEC-II(8)713>. 

Heteroaromatic Annulation with Cyclic Azaallyl Anions Synthesis of Bridgehead Nitrogen Heterocycles... 

The azaallyl anions 85.11-85.17 derived from cyclic nitrogen heterocycles generally react with 6 to afford the corresponding bridgehead nitrogen heterocycles. Some of the examples studied by our group are described below. 

Linke, S., Kurz,., Lipinski, D., and Gau, W., Annealation reactions of N-heterocycles to condensed pyridones with bridgehead nitrogen, Ann. Chem., 542, 1980. 

Similar studies have also been carried out on condensed heterocyclic systems with a bridgehead nitrogen. Indolizine [175] and its 2-methyl-, 1,2-, 2,6- and 2,8-dimethyl- and 1,2,3-trimethyl derivatives protonate preferentially on C-3 in trifluoroacetic acid, giving cations [176] (Fraser et al., 1962). In general, when position 3 is... 

In this article some heterocyclic (5,5)-fused systems with one bridgehead nitrogen atom will be reviewed. The survey given here is limited to those heterocycles that contain 10 jr-electrons and where atoms a and b are carbon (Scheme 1). 

HC(15)1247 W.L. Mosby, Heterocyclic systems with bridgehead nitrogen atoms. 

The general class of triazolopyridines includes five heterocyclic systems. Three have bridgehead nitrogen, compounds 1-3 and two do not, compounds 4 and 5. In general these two major divisions reflect differences in synthesis or in properties. Compounds 4 and 5 can exist in several tautomeric forms there is little direct evidence on the major tautomer, and the compounds are therefore shown throughout in the 1H form. 

W. L. Mosby, Heterocyclic Compounds. Systems with Bridgehead Nitrogen, Part 2. Wiley (Interscience), New York, 1961. 

No specific review of aromatic azapentalenes exists, though much of the work before 1960 is covered in a more general article on bicyclic heterocycles with bridgehead nitrogen atoms by Mosby6 in the Weissberger series on heterocyclic chemistry. That article makes no distinction between aromatic and saturated systems, and the present review, though not exhaustive, deals mainly with aromatic systems and covers most of the literature to the end of 1975. Nonaromatic compounds will not be treated except where they are sufficiently important. 

Of the condensed heterocycles containing a bridgehead nitrogen atom that have been subjected to the Anil Synthesis, the 2-arylimidazo[l,2-a]-pyridine system exhibits good alkali stability, whereas the 2-aryl-j-triazolo[l,5-a]pyridine system may only be reacted below 45°C.19,78... 

XII. Compounds from Heterocycles Containing Nitrogen at a Bridgehead... 

A different class of polycyclic naphthoquinone dyes is based on the n apht h 12,361 i ndolizine -6,11 -dione system 14, which is readily accessible by condensation of 2,3-dichloro-l,4-naphthoquinone with active methylene compounds in the presence of pyridine [22], or by reaction of 2-methoxy-3-pyridino-1,4-naphthoquinone with an active methylene compound [23], In 14, the bridgehead nitrogen atom acts as an effective auxochrome, and hence orange to red colors are observed without further substitution. Derivatives of 14 (R = amide group) are of particular value as vat dyes and pigments. Related isomeric heterocyclic structures have also attracted interest, e.g., 15, a yellow disperse dye for polyester [24],... 

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