Selenium, elemental reactions with

The treatment of vinyl anions with elemental selenium also leads to seleno-carbonyl compounds via eneselenolate anions (Eqs. 4-6). Deprotonation of l,3-selenothio-2-thione with EDA followed by the reaction with elemental selenium proceeds accompanied with the rearrangement of vinylic skeleton to form l,3-dithio-2-selone derivatives (Eq. 4) [38]. The vinyl anions from oxa-zolines and imidazoles were treated with elemental selenium to give the oxazo-line selone and imidazoline selone after the aqueous workup (Eq. 5) [39]. The reaction of vinyl magnesium halides with elemental selenium and allyl bromide gives allyl vinyl selenides that undergo a seleno-Claisen rearrangement to generate y,6-unsaturated selenoaldehydes (Eq. 6) [40]. 

The tetrachloroaluminate complexes are also derivable from halogenophosphoranes, RPCI4 (in turn preparable, in principle, from RPCI2 and Cl2 ) and AICI3. The complex from EtPCl4 reacts very slowly at 90-100 °C with H2S with the liberation of HCl and the ultimate formation of the species EtPS2 , but the stepwise process can be interrupted to allow the isolation of EtP(S)Cl2. More conveniently, a treatment of the complexes with sulphur, EtSH or KCNS, particularly in the presence of KCl (to remove the AICI3), leads to the thiophosphonic dihalides, RP(S)Cl2 a similar reaction with elemental selenium... 

Sulfur diamides (diaminosulfanes) are obtained by the action of sulfur chlorides with an aliphatic secondary amine (Eq. 10.10). ° The monoselanes Se(NR2)2 (R = Me, Et) have also been prepared. Polyselanes Scx(NR2)2 (x = 2 - 4, NR2 = morpholinyl x = 4, NR2 = piperidinyl) are formed in the reaction of elemental selenium with the boiling amine in the presence of Pb304. ... 

Cyclic selenoureas have been investigated. The 2-selenoimidazolines have been obtained from the reaction of imidazol-2-ylidenes with elemental selenium.246 2-selenouracil has been synthesized by condensation of selenourea with ethyl 3-ketohexanoate (Scheme 80).247... 

For the preparation of secondary and tertiary selenoamides, several methods have been used reaction of lithium alkyneselenolates (obtained using metallic selenium) with amines, aromatic diselenoic acid Se-methyl esters with amines or dihalomethane with elemental selenium, NaH and amines (Scheme 83).258 266... 

Thiotraamidophosphoric acids (35) are isoelectronic with phosphoric acids and were initially reported from the reaction of phosphorus pentasulfide with primary amines at high temperatures.62 Subsequently, an improved synthesis for 35 with increased yields and milder conditions has been reported involving the room temperature reaction of thiophosphoryl chloride and primary amines (Equation 50).63 The most convenient route to the analogous selenium derivatives SeP(NHPh)3 is from the oxidation of P(NHPh)3 with elemental selenium (Equation 51).63 Also isoelectronic with phosphoric acids are dithio wamido-phosphoric acids (36), which can be prepared from the reaction of phosphorus pentasulfide with an excess of primary amine at 30°C in toluene (Equation 52).62 The selenium derivatives of 36 can be prepared in a similar reaction from phosphorus (V) selenide, although due to their increased acidity... 

Formation of a new compound PSeF3 has been claimed in the reaction of PF3 with elemental selenium, at 300-400°C, identified from a mass spectrum analysis, showing the fragments (PSeF2)+ with the expected selenium isotopes (34). However, since no further data have been obtained, it appears very likely that the compound actually was... 

The tellurophene is formed via a first Te-C sp cleavage followed by an unusual Te-C sp cleavage. The treatment of the reaction mixture with benzaldehyde or with elemental selenium followed by ethyl bromide affords the 2-substituted teUurophenes. 

Reaction of Hg[Fe(CO)3NO] with elemental selenium in refluxing toluene (52) proceeds just like the reaction of this mercurial with elemental sulfur (36, 37) and gives the cubane-type tetranuclear cluster [Fe4Se4(N0)4]. This cluster can also be readily synthesized by reaction of Na[Fe4Se3(NO)7] with elemental selenium, also in refluxing toluene (53). 

Reaction of phosphaalkynes 209 with elemental selenium in toluene at 70 °C in the presence of triethylamine gave 1,2,4-selenadiphospholes 33 and 69-71 in 74-89% yield (Scheme 45) <1999S1642>. 

Diselenetane derivative 39 reacts with elemental selenium in the presence of a catalytic amount of triphenyl-phosphine or triphenylphosphine selenide to give 1,2,4-triselenolane 65 in 37% yield (Scheme 9) <2001TL3881>. The reaction with propiolic acid under reflux conditions in toluene affords selenodioxenone 66 (25%) and trace amounts of compound 67 <2004BCJ1933>. 

The reactions of /< //-butylarylmethylenetriphenylphosphoranes with elemental selenium yield the corresponding 1,3-diselenetanes 39 (24%) and 85 (26%) along with the 1,2,4-triselenolane derivatives 86 and triphenylphosphine selenide (Scheme 25) <2001TL3881>. 

The reactions of electrophiles with metallated aromatic compounds obtained in this way provide access to products that are not accessible at all or not selectively through classic Ar-SE reactions. Phenyllithium, for example, unlike benzene, reacts with ketones to form tertiary alcohols or with elemental selenium to form first phenylselenol and thereafter, through oxidation, diphenyl diselenide (Figure 5.35). 

The ability of carbanions to react with elemental selenium can be advantageously used for the synthesis of selenocarbonyl compounds. For example, sulfur ylides 201 (E = +SMe2) have been reacted with elemental selenium to generate the corresponding selenocarbonyl compounds 202 (Scheme 59).374,375 But Staudinger selenylation also has been applied to the synthesis of selenoketones 202 from phosphorus ylides 201 (E = +PPh3), which have been trapped by dienes in hetero-Diels-Alder reactions.376-383... 

Alkynyl anions can be reacted with elemental selenium to form alkynylselenolates 203. These alkynylselenolates 203 have been used as key intermediates for the synthesis of a variety of selenocarbonyl compounds. First reactions have already been carried out earlier,384 and some later improvements widened the scope of this reaction including the synthesis of selenoesters, selenothioesters, and selenoamides of type 204 (Scheme 60).385,386 Even a direct... 

A few three-component reaction sequences leading to selenophenes have been reported. Lithiation of diphenylace-tylene followed by treatment with elemental selenium led to 2,3,4,5-tetraphenylselenophene 121 (Equation 20) <1999JOM(573)267>. 

It was recently found that selenium dichloride can conveniently be prepared by the reaction of elemental selenium and SO2CI2 It is relatively stable in coordinating solvents and can be used as a reagent for synthetic applications. The attempt to prepare TeCb in the analogous manner from elemental tellurium and SO2CI2 resulted in the formation of various chloridoteUurate anions with different counterions. The solvent and the possible presence of a small amount of residual moisture probably determine the identity of the main product in each individual case. 

Dimethylaluminum methylselenolate (38) is prepared in situ by the reaction of trimethylaluminum with elemental selenium in refluxing toluene [66]. The yellow-colored solution can be used in various reactions, such as the conversion of esters to the corresponding selenol esters, the ring opening of epoxides, and Michael addition to cyclohexenone (Scheme 36) [66]. 

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