Heterocyclic compounds chalcogen heterocycles

The structures of chalcogen-nitrogen compounds are frequently unpredictable. For example, the reactions of heterocyclic systems often result in substantial reorganization of their structural frameworks, e.g. ring expansion or contraction. The formation of acyclic products from ring systems (or vice versa) is also observed. 

The reactions of heterocyclic chalcogen-nitrogen systems often result in substantial reorganization of their structural frameworks. Spectroscopic techniques alone are rarely sufficient to provide decisive structural information, and X-ray crystallography has been of paramount importance in the development of chalcogen-nitrogen chemistry. The structural chemistry of Se-N and Te-N compounds has been reviewed.19... 

A very large number of heterocyclic compounds are known consisting solely of phosphorus and chalcogen atoms, as well as those containing phosphorus, chalcogen and carbon or other hetero atoms. Such heterocycles have been the subject of several reviews2,83,84 and the discussion here will be limited to some representative examples of these compounds. 

Diathiadiphosphetane disulfides are probably the most studied and the most thermally and hydrolytically stable of all the phosphorus-chalcogen heterocycles. They contain a central four membered P2S2 ring and can be prepared from heating phosphorus pentasulfide with aromatic compounds. The most well-known of these is Lawesson s reagent (43), which is made from anisole and phosphorus pentasulfide,92 and is used extensively in organic synthesis procedures (see Section 5.4.1). Other dithiadiphosphetane disulfides of note are 44 and 45, formed from the reaction of phosphorus pentasulfide with ferrocene or 1 -bromonaphthalene respectively.93... 

The reaction of silylenes 83 and 85 with the chalcogens S, Se, Te resulted in the formation of the respective four-membered heterocycle 102 (Scheme 8) <1996JOM211, 1998JA12714>. For the reaction of silylene 83 with 1 equiv of sulfur low-temperature NMR studies suggest the formation of silanethione 103 which then dimerizes. Reaction of excess sulfur with silylene 83 results in the formation of compound 104 with simultaneous release of the diimine ligand. 

Sulfur and selenium heterocycles have also been prepared by reaction of zirconium-benzyne complexes with the elemental chalcogens. In these reactions, chalcogens insert into both of the zirconium-carbon bonds (Scheme 7).53-55 Interestingly, neither para-bromo norpara-dimethylamino substituents in 65 interfere with their conversion to 66 (60-80% yields).54 Complexes 66 react further with mono- and bifunctionalized electrophiles (Scheme 7) to yield ort/io-dichalcogenated benzenic compounds 67-69. 

Professor A. Haas (Bochum, Germany) deals with some of the recent developments in chalcogen-heterocycles with particular emphasis on simple sulfur, selenium, and tellurium compounds that can serve as synthons for the preparations of various heterocycles. 

By analogy to the formation of 1, heterocyclic silicon chalcogen derivatives can be synthesised by the reaction of bifunctional silicon halogen compounds RR SiCl2 with Na2E (Eq. 3). 

The transition-metal chemistry and nature of the complexes formed with As-As bonded compounds has been reviewed. The reader is referred to this comprehensive review for an overview of the nature of complexes that contain chains of coordinated R-As units, heterocyclic As-chalcogen rings, and unsubstituted arsenic atoms and for references to the primary literature. The limited transition-metal chemistry of the phosphaarsenes and diarsenes is also reviewed. ... 

J. Albertsen, Synthesis and characteristics of new chalcogen-rich heterocycles with organoelement compounds of the 4th main group and purification of bisorganic polysulfanes using titanocene chalcogenide chelate complexes. Doctoral Dissertation, Technical University of Berlin, 1993. 

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