Parent Selenium Compounds

We do not know if exposure to selenium will result in birth defects in people. Selenium compounds have not been shown to cause birth defects in humans or in other mammals. We have no information to suggest that there are any differences between children and adults in where selenium is found in the body or in how fast it enters or leaves the body. Studies in laboratory animals have shown that selenium crosses the placenta and enters the fetus. Studies in humans show that infants are supplied with selenium through breast milk, and therefore, women who were exposed to selenium by living near a waste site might transfer selenium to their babies. However, babies in areas of China with high selenium in the soil did not show any signs of health effects due to selenium, even though some of their parents did. 

The sulfur analogs of these selenium compounds react less efficiently with benzyne. Thus the yield of396 (S in place of Se) was only 5% from the benzothiadiazole. However, with the parent thiadiazoles 406 the yields are improved. Thus 1,2-benzoisothiazoles 409 are formed in 25-75% yield, depending on probably by the mechanism shown. Selenium... 

Furalazine, Acetylfuratrizine, Panfuran-S. Heating nitrovin in butanol or dimethylformamide at 100—130°C affords furalazine, 6-[2-(5-nitro-2-furanyl)ethenyl]-l,2,4-triazine-3-amine (34). An improved synthesis originates with 5-nitro-2-furancarboxaldehyde and acetone, proceeds through 4-(5-nitro-2-furanyl)-3-buten-2-one followed by a selenium dioxide oxidation to the pymvaldehyde hydrate, and subsequent reaction with aininoguariidine (35). Furalazine, acetylfuratrizine (36), and the A[-A/-bis(hydroxymethyl) derivative, Panfuran-S, formed from the parent compound and formaldehyde (37), are systemic antibacterial agents. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Simple derivatives of the parent compound in this group, exo,endo- and o ,o -2,6-dimethyl-l-phosphabicyclo[2.2.1]-heptane 211 and 212, have been synthesized by the cyclization of 2-methyl-4-(2-propenyl)phospholane in the presence of base <2002ZFA580>. The structures were determined via spectroscopic means as well as X-ray crystallography and further confirmed by reactions with selenium, sulfur, (CH3)2SeO, CH3I, and HS03F. 

Coordination of [(t-C4H9)2P(=Se)I] with molecular iodine furnishes a 1 1 adduct that crystallises as cyclic dimer in the solid state (Figure 46).57 From each I2 molecule within the structure, one atom acts as acceptor towards selenium, and the other one becomes very weak donor towards the iodine atom bonded to phosphorus. This compound fulfills the requirements of a soft-soft base pair . As in the structure of the parent donor molecule [(t-C4Hg)2P(=Se)I],... 

In the course of the quest for new Fe(III) spin crossover compounds, systems related to N,N-disubstituted-dithiocarbamates have been explored. This section deals with oxygen and selenium derivatives of this parent ligand system, as displayed in Fig. 2. 

The known nonclassical A,B-diheteropentalenes consist of compounds containing an annelated thiophene or selenophene ring, the only uncharged nonradical representations of which contain a tetravalent sulfur or selenium, while the charged structures represent carbonyl, azomethine, thiocarbonyl or selenocarbonyl ylides. The parent systems have not yet been synthesized, only substituted compounds being known. The properties of these substituted derivatives provide a good measure of understanding of the reactivities of the parent systems. 

Mass spectral fragmentation patterns in the spectra of these compounds are in accord with the formation of alkynes. The first step in the fragmentation of 1,2,3-selenadiazoles is the loss of N2 followed by extrusion of selenium and formation of the corresponding alkyne. The abundance of the alkynic ion in the mass spectrum appears to be dependent on the nature of the substituent group present in the selenadiazole. When the alkynic ion cannot be stabilized by the formation of a cation on the adjacent carbon atoms, the abundance of the alkynic ion decreases (10% in the parent compound and zero for 4-f-butyl-l,2,3-selenadiazole). On the basis of the mass spectral pattern it is possible to predict the yield of the alkynic compound formed through pyrolysis or photolysis of a given... 

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