Group 15 Heteroatoms

I 3.4 Borane Clusters with Group IS and Group 16 Heteroatoms Survey of Compounds and Structures... 

The ni-11 dusters with their typical monocapped pentagonal-antiprismatic structure (Figure 3.4-9) have been comprehensively investigated. The group 15 and group 16 heteroatoms are generally found in the 4k positions of the pentagonal aperture. 

There is a lack of experimental evidence for ar-6 and ar-7 clusters with group 15 and group 16 heteroatoms. 

The syntheses from [4+1] atom fragments, in which the Group 16 heteroatom is introduced between two nitrogen atoms, are the most widely applicable and versatile methods available for construction of the 1,2,5-thiadiazole ring system. These methods have been applied to the synthesis of monocyclic and polycyclic aromatic forms of these ring systems in addition to the direct formation of 1-oxides and 1,1-dioxides, 2-oxides, quaternary salts, and reduced forms. The earliest use of the [4+ 1] synthesis dates back to 1889 when Hinsburg prepared 2,1,3-benzothiadiazole (I) from o-phenylenediamine and sodium bisulfite. 

Not only alkyl hahdes but also group 16 heteroatom compounds are reduced with Sml2 upon photoirradiation. This Smh-hi system is extremely effective for the reduction of organic selenides. On the other hand, the photoinduced reduction of sulfides with Smij does not proceed at all, while dodecane is obtained in 38 % yield by the photoinduced reduction of dodecyl phenyl telluride with Sml2 (Scheme 2.35) [95]. 

Scheme 2.35 Photoinduced reduction of group 16 heteroatom compounds...

Modes of attachment of functional groups to crosslinked polystyrene are discussed ( 1). Attention is drawn to improved stability and activity of polymer-bound reagents and catalysts incorporating dimethylene spacer between polystyrene aryl and functional group heteroatom, and the simplicity and versatility of their synthesis through high-conversion functional group modifications. 

All metal vinylidenes described herein are derived from alkynes. While alkyne-to-vinylidene interconversion typically occurs via the 1,2-shift of a hydrogen atom, the corresponding migration of heavier main group heteroatoms is also possible. 

Substitution of the carbon-silicon bond in allyl- and vinylsilanes by an electrophile has served as a powerful tool in organic synthesis. Electrophiles ranging from proton, carbon and main group heteroatoms to certain transition metal species have been employed. A... 

Nicholls, J. N. Main group heteroatoms in transition metal clusters, Polyhedron 1984, 3, 1307. 

Heterocumulenes are compounds with a substructure X=C=Y, in which at least one of the groups X or Y is an O atom, an S atom, or an NR group. Heteroatom nucleophiles add to heterocumulenes, as was already discussed briefly with respect to the C=0-containing heterocumulenes in Section 6.1.1. Most of the heteroatom nucleophiles used are not charged. 

An extension of the synthetic applicability of lithium halomethanes is achieved by the simultanous presence of another main group heteroatom at the same carbon. Thus, if one of the chlorine atoms of dichloromethyllithium is replaced by a sulfonylamin group, the following products are obtained by reaction with electrophiles (Eq. (23)) 25). The substituted carbenoid can be converted to normal carbonyl adducts as well as to olefins and cyclopropanes. 

A wide variety of main group heteroatom-containing ring systems are formed by the reaction of appropriate reagents with metallacycles derived from cycloaddition of Cp2Zr with alkynes, diynes, dienes, enynes or alkynenitriles. This is an exceptionally general process of considerable potential, especially for the synthesis of less-common types of heterocycles (Schemes IS and 16). ... 

As for tetranuclear clusters, pentanuclear transition metal clusters are only capable of partially encapsulating a main-group heteroatom. The c/o5o-pentanuclear cluster, the trigonal bipyramid, has an interstitial cavity of similar dimension to that of the tetrahedron, and must therefore open-up if it is to accommodate a semi-interstitial atom. The most commonly observed M5E clusters (E = main-group atom) adopt square based pyramidal structures, which can be derived from the trigonal bipyramid by M-M bond cleavage or can, alternatively, be viewed as /i/Jo-octahedral species (Scheme 2). 

Homolytic substitution at higher main group heteroatoms to give Se-, Te-, and P-heterocycles 06CC4055. 

We have progressed from a discussion of obvious neighboring groups, heteroatoms with nonbonding electrons, to less obvious internal nucleophiles, the filled n orbitals of double bonds. In every case, a pair of internal electrons does an initial intramolecular Sn2 displacement, which is followed by a second, external (inter-molecular) Sn2 reaction. The result is overall retention of configuration. 

In addition to the alkynylation of second and third row main group heteroatoms, there are a few examples of alkynylation of heavier elements including arseiuc [85], selenium, and tellurium [84, 86, 87]. 

If there are heteroatoms in polyene component they are to be replaced by their isoelectronic carbon groupings. Heteroatoms offer the possibility of new reactions by the non-bonding pair of electrons or by the availability of low-lying imoccupied orbitals. This type of interactions should be considered cautiously. 

Figure 10.3-40. The rating for the disconnection strategy carbon-heteroatom bonds is illustrated, Please focus on the nitrogen atom of the tertiary amino group. It is surrounded by three strategic bonds with different values. The low value of 9 for one ofthese bonds arises because this bond leads to a chiral center. Since its formation requires a stereospecific reaction the strategic weight of this bond has been devalued. In contrast to that, the value of the bond connecting the exocyclic rest has been increased to 85, which may be compared with its basic value as an amine bond.

The graphic interface is a multitasking environment that works well. The protein and carbohydrate builders are particularly convenient to use. The small-molecule builder has a selection of common organic functional groups as well as individual atoms for organics and common heteroatoms. There are a... 

The authors (85) have also mentioned the deformational vibrations (7) of the out-of-plane group -CH= of a pentatomic heterocyclic nucleus, showing that there exists a relationship between the absorption frequencies of this group and the electronegativity of the heteroatom (86). 

A large group of heterocyclic aromatic compounds are related to pyrrole by replacement of one of the ring carbons p to nitrogen by a second heteroatom Com pounds of this type are called azoles... 

Substitutive Nomenclature. The first step is to determine the kind of characteristic (functional) group for use as the principal group of the parent compound. A characteristic group is a recognized combination of atoms that confers characteristic chemical properties on the molecule in which it occurs. Carbon-to-carbon unsaturation and heteroatoms in rings are considered nonfunctional for nomenclature purposes. 

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