Heterocycles containing Other Atoms

Cyclization of the dichlorosilane (381) has given a 30% yield of l,l-dichloro-2-methylsilacyclohexane (382). Silacyclohexadienes such as (383) reacts with dihalogenocarbenes to give adducts at either of the double-bonds, depending on the character of 1-Arsanaphthalene (384) has been synthesized from 

Arbuzov, O. A. Erastov, S. S. Khetagurova, andT. A. Zyablikova, Izv. Akad. Nauk SSSR, Ser. Khim., 1979, 2136. 

Space limitations dictate that this is a selective ( 50%) rather than a complete review in particular, papers and patents where the main objectives were pharmacological rather than chemical have been omitted. 

Several useful general reviews on seven-membered heterocycles have appeared in advanced texts,and there are also reviews on dihydrodiazepines and their salts, dibenzoxazepines, thiepins, fluorinated tricyclic neuroleptics, and the electrochemistry of substances of pharmacological importance (including dibenzodiazepines).  

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IV. Heterocycles Containing Other Elements in the Ring along with Te and N Atoms... 

The rate constant data have been divided into three major sections, namely absolute rate constants, relative rate constants, and isotope effects. The subgrouping is given in the list of contents. It is essentially based on a separation of radicals derived from aliphatic and other nonaromatic compounds from radicals which are formed from substrates containing aromatic and/or heterocyclic constituents. Within these two subgroups it seemed useful to further distinguish between radicals composed only of C and H atoms and radicals containing other atoms as well. 

Aromatic rings can also contain heteroatoms. Pyridine, C5H5N, for example, is a six-membered ring nitrogen heterocycle (contains an atom other than carbon in the ring). Like benzene, each atom of the ring is sp hybridized, and... 

Unlike carbocyclic (or homocyclic) hydrocarbons which have been discussed previously, heterocyclic compounds contain in their rings other atoms, such as nitrogen, oxygen, or sulfur, in addition to carbon. Some examples are shown below ... 

Aromatic heterocycles containing two nitrogen atoms are best reduced by catalytic hydrogenation. Other reduction methods may cleave some of the rings. Even catalytic hydrogenation causes occasional hydrogenolysis. 

The final chapter in this volume covers the use of sulfur monochloride in the synthesis of heterocyclic compounds and is by O.A. Rakitin and L.S. Konstantinova (Zelinsky Institute, Moscow, Russia). It includes a survey of the extensive work carried out by these authors and other friends and associates of the late Charles Rees on heterocycles containing heterocycles with up to five sulfur atoms and often many nitrogen atoms. In addition, the chapter also shows how sulfur monochloride may be used advantageously in the synthesis of other sulfur heterocycles. 

As discussed in Chapter 3, some other inorganic polymers also contain phosphorus atoms.47 They are derived from the basic phosphazene structure described in Chapter 3, and are obtained by the ring-opening polymerization of heterocyclic compounds in which one of the disubstituted phosphorus atoms is replaced by another moiety. Specifically, introduction of a carbon atom can yield poly(carbophosphazenes), with the repeat unit shown in 6.49. Alternatively, replacement with a sulfur atom can yield a poly(thiophosphazene) (6.50). Relatively little is known about these polymers at the present time 47... 

VI. Reductions of Other Heterocycles Containing One Nitrogen Atom... 

Very few structural investigations have been made for five-membered heterocycles containing selenium or tellurium and one other chalcogen atom by either theoretical methods or X-ray diffraction. The lone theoretical treatment <8lJST(7l)l) was a MINDO/3 optimization of molecular geometry for l,3-thiaselenole-2-thione and -2-selenone and for 1,3-diselenole-2-selenone (8) and -2-thione. These molecules were predicted to be planar. The calculated bond lengths and angles for (8) are shown in Scheme 3. 

The syntheses of monocyclic five-membered heterocycles containing one selenium or tellurium atom and one other chalcogen atom can be classified into four groups, according to the number and types of building blocks required to form the ring in a one-step process ... 

Table 15 Ring Syntheses of Five-membered Heterocycles containing One Selenium or Tellurium and One Other Chalcogen Atom ...

The reaction between stannylenes and carbon-carbon multiple bonds generates unsaturated heterocycles containing tin and between two and four other atoms (Scheme 2). Formation of five-membered rings from [4 + 2] addition reactions are by far the most common (43). With the isolated, strained alkynes 11 and 12, both 1-stannacyclopropene (13) and... 

To limit the size of this report, a restriction was placed on the compounds that were eligible for inclusion. Firstly, to be included, the compound had to contain at least one five-membered heterocycle in its structure. Secondly, the number of atoms in the internal ring pathway of the macrocycle was required to contain at least 17 atoms (one more than the number of atoms present in the inner core of porphine Fig. 1). Thus this definition, which is in two parts, eliminates conjugated macrocycles containing other small heterocycles such as pyridines. It also rules... 

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