Systems containing Nitrogen as the only Heteroatom

3 Macrocycles Other than Crown Ethers Systems containing Nitrogen as the only Heteroatom. - The aza[18]annulene (35) has been synthesized by photolysis of (36) at — 80°C. Aza[14]-annulenes have been prepared by the same route. An efficient route to 

Macrocyclic polyamines are assuming a role of increasing importance as models for biological systems. Fifteen- to eighteen-membered macrocycles that bear four to six amine moieties form stable 1 1 complexes with inorganic phosphates, AMP, ADP, and ATP, and the macrocycles play a valuable role in the study of the binding of phosphate in vivo. The com- 

A general route to tri- and hexa-aza-macrocycles has been reported, using monotosylated ethylenediamine with TV -tosylaziridine. The product was treated with benzoyl chloride, and was converted into the disodium salt. The cyclization was effected by reaction with bisulphonate esters. Hexa-aza-macrocycles have also been prepared by condensing disulphonamide salts of the tritosylated diethylenetriamine with disulphonate esters.  

There have been further developments in the study of octopus cyclo-phanes as models for enzymes, schematically shown in (43). Thus (44) incorporates not only uncharged hydrophobic, spin-labelled, and fluorescent probes, but also anionic compounds, including bulky dyes. It may selectively catalyse the hydrolysis of p-nitrophenyl carboxylates that bear long alkyl chains. The tricyclic lactam (45) exists in solution as slowly ring-inverting 

Murakami, A. Nakano, K. Akiyoshi, and K. Fukuya, J. Chem. Soc., Perkin Trans. 1, 1981,2800. 

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Systems Containing Nitrogen as the Only Heteroatom.- A useful... 

Systems containing Nitrogen as the only Heteroatom.—One Nitrogen Atom. The aza[14]annulene (28) has been synthesized by the photolysis of (29) in pentane at —70°C. Its aromatic character is demonstrated by the large difference in chemical shifts of the three inner and the ten outer protons of ca 9.5 p.p.m. Variable-temperature H n.m.r. moreover demonstrates that the ring is confor-mationally mobile, producing an equilibrium of two degenerate species. 

Of the various possible bicyclic 6-6 systems with one ring junction nitrogen atom dealt with in this chapter, the rings containing only nitrogen as the other heteroatoms have been most explored in the literature. The heterocyclic systems reported so far are shown the parent systems are named, but the actual compounds, mainly oxo derivatives, are drawn below 4/7-pyrazino[2,l-c]... 

Other studies (see, e.g., ref. 187c and references cited therein) have revealed that, in systems containing only O and N as heteroatoms, the azide form 184 is usually the only isomer observable in solution or in the solid state, whatever the position of the heteroatoms. Recent work has shown that the tetrazole forms are predominant in systems containing only nitrogen as the heteroatom in two special cases. If a proton is removed from the azide (e.g., 305), the anion 306 cyclizes to the tetrazole 306b. The cyclized form is likewise formed from the anions of azido-indazoles, -imidazoles, and -benzimidazoles but cycliz-ation is only partial with s-triazoles and negligible with tetrazoles. It is possible to trap the cyclized anions (e.g., 306b) by methylation - (Section IV,C,2) and obtain stable pyrazolo[l,5-rf]tetrazoles, 307 and 308. 

An important conclusion from the analysis of compounds discussed above is that all systems containing ring heteroatoms and 571 -hybridized ring carbon atoms only are virtually planar. This analysis is valid not only for the cationic system of (129) but also for non-cationic systems with ring junction nitrogen atoms and containing additional ring heteroatoms, such as (121), (122), (124), (126), (127), (130), (131), and (132). 

Coke-oven tar is an extremely complex mixture, the main components of which are aromatic hydrocarbons ranging from the monocyclics benzene and alkylbenzenes to polycycHc compounds containing as many as twenty or more rings. HeterocycHc compounds containing oxygen, nitrogen, and sulfur, but usually only one heteroatom per ring system are present. Small amounts of paraffinic, olefinic, and partly saturated aromatic compounds also occur. 

From the general structure of 1,2-diheterocines 1 with identical heteroatoms other than the scries with two nitrogen atoms (X — NR, which have already been discussed in Section 1.2. as they can be regarded as 1,2-dihydro-l, 2-diazocines), only one other example of such a 1,2-di-hcterocine system exists i.e. dibenzo derivative 4 containing the 1,2-dithiocin system 2.1... 

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