Systems containing Heteroatoms Other than Nitrogen

In order to overcome unfavourable entropy effects which lead to the formation of polyethers from o)-hydroxy-carboxylic acids, rather than lactonization, a rapid intramolecular esterification process, under mild conditions, has been developed 

Sternbach, M. Shibuya, F. Jaisli, M. Bonetti, and A. Eschenmoser, Angew. Chem., Int. Ed. Engl., 1979,18,634. 

Inanaga, K. Hirata, H. Saeki, T. Katsuki, andM. Yamaguchi, Bull. Chem. Soc. Jpn., 1979,52,1989. 

The complex formed between 4S—CH2CH2CH2 4 and Hg (C104)2 is the most stable complex yet known that involves Hg and a macrocyclic thioether. The X-ray structure indicates the presence of very little strain, yet even more stable complexes (by a factor of 10) are formed with the open-chain compound (MeSCH2CH2SCH2)2CH2, so that previous explanations of the macrocyclic effect are inadequate when applied to Hg . 

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Three bicyclic ring systems, pyrido[l,2-c][l,3,2]oxazaborine, pyrido[l,2-c][l,3,2]phosphorine, and pyrido[ 1,2-c]diazaphosphorine, have been described which contain as extra heteroatoms at least one heteroatom other than nitrogen, oxygen, or sulfur. Benzologues of these systems have not been reported. 

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... 

In a more general approach toward pentacyclic heteroaromatics from tricyclic ketones, treatment of the N-methylated derivative of 112 with p-tolylhydrazine, followed by Fischer indolization of the resulting phenylhydrazone in a mixture of trifluoroacetic acid and acetic acid, produced only a low yield of 114, although this method proved to be considerably mrae efficient for synthesis of analogous systems containing other heteroatoms than nitrogen (98SC1239). 

Any ring system containing at least one heteroatom (i.e. an atom other than carbon - typically nitrogen, oxygen, or sulphur) can be described as heterocyclic. This broad definition encompasses both aromatic heterocycles (such as pyridine 5.1) and their non-aromatic counterparts (piperidine 1.7). 

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... 

This chapter provides an update of Chapter 8.33 in CHEC-II(1996) <1996CHEC-II(8)863>. The work carried out on the bicyclic ring systems with ring junction P, As, Sb, or Bi has focused primarily on phosphorus. Very little work has been done on the other heteroatoms and as such the synthesis and reactivity of these compounds have been reviewed as one section, Section 12.12.7. Most of the compounds in this class contain more than one heteroatom, the additional atoms usually being oxygen and nitrogen. 

In systems that contain more than two heteroatoms in the same ring, the trends in properties that this book describes are taken to fnrther extremes. In particular, the additional heteroatoms, in both six- and flve-membered systems, lead to a snppression of electrophilic substitution and a slowing of electrophilic addition to nitrogen. On the other hand, fnrther increases in tendencies for nucleophilic substitution and addition, and in the five-membered componnds further increases in acidities of M-hydrogen, are found. 

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