Selenocarbonyl compounds reactions with

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... 

The reactions of selenocarbonyl compounds with electrophiles are also well-established procedures. Alkylations or acylations of the selenium atom of selenoamides409 or selenoureas410 are known. Selenonium salts are formed initially they can then be converted into diselenides, selenazoles, or cyclic selenides depending on their structure. Reactions of selenocarbonyls with bromine and iodine have also been widely exploited. Selenocarbonates, sele-nothiocarbonates,411-415 and selenoureas416-418 can be employed, the reaction of 209 with 1 equiv. bromine led to the hypervalent 10-Se-3 complex 210, whereas an excess of bromine gave rise to a cleavage of the carbon-selenium double bond and formation of product 211 (Scheme 64). 

The reactivity and reaction patterns of selenocarbonyl compounds vary considerably from the compounds in categories A-C in Scheme 1. The substituents adjacent to the selenocarbonyl group attenuate the polarity of the compounds. As a result, less polar selenoaldehydes and selenoketones behave as olefins, and the carbon selenium double bond of heteroatom-substituted selenocarbonyl compounds becomes more polar. In this section, a variety of transformations of selenocarbonyl compounds have been classified based on the reagents reacted with selenocarbonyl compounds. 

The interaction of selenocarbonyl compounds with inorganic metals and metal salts has been examined for three different purposes. First, the reaction of ... 

Alternatively, the reaction of isolated selenocarbonyl compounds with transition metal complexes has been applied to the synthesis of metal complexes of type 53. The complexation of furanselenoamides and thiopheneselenoamides to Pd, Rh, and Ru halides is accompanied with cyclometallization (Eq. 30) [111]. The formation of Cu [112a], Ag, Au [112b,c], Zn, Cd [113], Co [114], Cr, Mo, and W [115] complexes has been attained by reacting selenourea or selenoamides with the corresponding metal halides or metal carbonyls. 

Although some reactions, such as the transformation of -hydroxyalkyl selenides to -haloalkyl selenides (Scheme 161, b) or to vinyl selenides, enones (Scheme 161, 0. a,a-dihalocyclopropanes (Scheme 162, f) or p-hydroxyalkyl halides (Scheme 161, h Scheme 162, g), have bwn occasionally described or found only with specific types of -hydroxyalkyl selenides, especially those having a strained ring [e.g. their transformation to allyl selenides (Scheme 163, b), 1-selenocyclobutenes (Scheme 163, c) and cyclobutanones (Scheme 163, f),i2.i59,i60.i63] odiers are far more general. This is particularly the case of eir reductions to alcohols (Scheme 161, a Scheme 162, a Scheme 163, a Scheme 164, a Scheme 165, a) - or alkenes (Scheme 161, c Scheme 162, c Scheme 163, d Scheme 164, c Scheme 165, a Scheme 166, c), 89,i94,239 transformation to allyl alcohols (Scheme 161, e Scheme 162, b Scheme 164, b Scheme 166, b), - epoxides (Scheme 161, g Scheme 162, d Scheme 163, e Scheme 164, d Scheme 165, b Scheme 166, d) and rearranged carbonyl compounds (Scheme 162, e Scheme 164, e Scheme 165, a, c Scheme 166, e), - as well as oxidation to a-selenocarbonyl compounds (Scheme 161, d). 2 2.248-25i... 

The reaction of selenium with CO and H2O in fhe presence of tertiary amines generates amine salts of hydrogen selenides ([HSe ]- [R3NH], =1 or 2), which can be used for the synthesis of selenium compounds such as selenides, diselenides, and selenocarbonyl compounds and for fhe selective reduction of carbonyl, nitro, and olefinic compounds [118]. 

The interaction of selenocarbonyl compounds with inorganic metals and metal salts has been examined for three different purposes. First, the reaction of selenoamides [104],selenothioacetic acid S-esters [105],anddiselenoesters [85] with Cu, Ybl2/Yb, Sml2/Sm, NiCl2, or Cd(OAc)2 proceeds with the extrusion of ... 

The [2+4] cycloaddition of selenocarbonyl (selenoxo) or tellurocarbonyl (telluroxo) compounds to diene systems remains one of the most widely used reactions for the preparation of various six-membered rings containing selenium or tellurium (see CHEC-II(1996), Section 5.11.7.2.1). The extremely sterically hindered selenal 154 has been isolated in monomeric form in solution and reacts with 2,3-dimethylbutadiene to afford the corresponding dihydro-selenin cycloadduct 155 (Equation 62) C1996AGE660, 1997T12167, 1998PS633>. 

The laboratories of Stec (24) and the author (26-28) have reported that the nitrogen anions of phosphoramidates react with carbonyl compounds (benzalde-hyde or CO2) to incorporate an atom of oxygen bonded to phosphorus at the expense of the nitrogen substituent, and that this reaction proceeds with retention of configuration at phosphorus. This stereochemically useful reaction, known as the Wittig-Staudinger reaction, is not limited to carbonyl compounds but can also be used with thiocarbonyls or selenocarbonyls to produce chiral phospho-rothioates or phosphoroselenates with retention of configuration at phosphorus (27). The primary application of this reaction has been in the preparation of both... 

Dialkyl triselenocarbonates have been characterized as ambident electrophiles by Henriksen and Kristiansen on the basis of their study of the reaction of these compounds with amines. In general, this reaction resulted in the formation of various products, a fact that was rationalized by the application of Pearson s principle of hard and soft acids and bases. Thus the selenocarbonyl carbon atom was found to represent the harder centre of acidity, combining principally with the harder amine base added, whereas the selenium atom of the alkylseleno-group appeared to represent a softer centre of acidity, combining preferentially with the softer alkyl selenide ion liberated by the former process. 

---