Selenylation

Diselenides can also be oxidatively fluorinated, as shown in equation 18 [118, 119], Benzene selenyl fluoride is postulated as an intermediate during the fluo-roselenation of alkenes with diphenyl diselenide and xenon difluotide [73, 120]... 

Selenium Nitride (Nitrogen Selenide). Se4N4, mw 371.87, N 15,07%, yel-brick red hygr amorph powd, mp (expl 160—200°), bp (decompn). SI sol in hot w (decompn) v si sol in acet, acet ac, bz CS2. Methods of prepn include passing dry ammonia into a dil soln of selenyl chloride in bz, or into a cooled soln of selenium chloride in CS2 (Refs 1-5 7-10)... 

Sulfenylation, Sulfonation, and Selenylation of Ketones and Carboxylic Esters... 

For reviews of selenylations, see Back, T.G. in Liotta Organoselenium Chemistry, Wiley NY, 1987, p. 1 Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis Pergamon Elmsford, NY, 1986, p. 95. 

Selenylation can also be done under conditions in which another nucleophilic component of the reaction captures the selenium-bridged ion. For... 

Terminal alkenes react with selenenyl halides with Markovnikov regioselectivity.64 However, the (J-selenyl halide addition products readily rearrange to the isomeric products.65... 

An analogous reaction occurs when allylic selenoxides are generated in situ by oxidation of allylic selenyl ethers.277... 

An exchange reaction between Se02 and SeCl4 produces selenyl chloride. 

Although such reactions must take place to only a very slight extent, autoionization of thionyl chloride and selenyl chloride is presumed to produce EOCl+ and FOCI, ions. The molecules are pyramidal in the gas phase, but there is extensive bridging between molecules in solid SeOCl2. 

The conversion of the polystyrene-supported selenyl bromide 289 into the corresponding acid 290 allowed dicyclohexylcarbodiimide (DCC)-mediated coupling with an amidoxime to give the 1,2,4-oxadiazolyl-substituted selenium resin 291 (Scheme 48). Reaction with lithium diisopropylamide (LDA) and allylation gave the a-sub-stituted selenium resin 292, which was then used as an alkene substrate for 1,3-dipolar cycloaddition with nitrile oxides. Cleavage of heterocycles 293 from the resin was executed in an elegant manner via selenoxide syn-elimination from the resin <2005JC0726>. 

Sulfenyl chlorides and halogens react with 1,2-alkadienylphosphonic acids to afford phosphorus-containing heterocydes [72], However, the electrophilic addition of dialkyl 4-methyl-2,3,5-hexatrien-2-yl phosphonates with sulfenyl or selenyl chloride afforded 2-thienyl methylphosphonates or the seleno analogues [73, 74]. The conjugate addition of sulfenyl or selenyl chloride with the 2,4-diene moiety in the starting allene leads to the formation of the five-membered skeleton (Scheme 10.69). 

The phenylselenyl radical adds irreversibly to the central carbon atom of 2-methylbuta-l, 2-diene (Id) with a rate constant of 3 x 106 M-1 s-1 (23 1 °C) (Scheme 11.7) [45], On a synthetic scale, PhSe addition to cumulated Jt-bonds has been investigated by oxidizing phenylselenol with air in the presence of mono-, 1,1-di- or 1,3-di-substituted allenes to provide products of selective fi-addition. Trapping of 2-phenyl -selenyl-substituted allyl radicals with 02 did not interfere with the hydrogen atom delivery from PhSeH (Scheme 11.7) [31]. 

In the above-described displacement reactions (Sh2) of sulfur- and selenium-containing compounds, the mechanism could either be a synchronous or a stepwise process (Scheme 4.2). Thus, in the Sh2 stepwise mechanism an intermediate sulfuranyl or selenyl radical is formed, followed by a-cleavage [56]. Based on competitive studies, a stepwise process was suggested to occur in the reaction of (TMS)3Si radical with -decylphenylselenide [43]. On the other hand, ab initio calculations supported the synchronous process and the same observations were explained in terms of an overall reversible reaction [57]. 

Scheme 10.12 gives other examples of cyclization, including examples in which radicals are generated by sulfuryl and selenyl abstraction and by Mn(02CCH3)3 oxidation. 

Thiyl and selenyl radical-mediated domino reactions of dienes... 

DOC (dissolved organic carbon), 606, 607-8 Dodecyltrimethylammonium bromide, 744 Domino reactions, thiyl and selenyl radicals, 221-3, 224, 225, 226-7 DOPA (3,4-dihydroxyphenylalanine), 614, 615... 

Selenophenes, dioxirane oxidation, 1157 Selenyl radicals, triplet oxygen domino reactions, 223, 227... 

The full account of the use of sulphenylation-dehydrosulphenylation for the introduction of a -unsaturation into carbonyl compounds includes some steroidal examples. The similar selenylation-dehydroselenylation of 17-oxo-steroids resulted in the formation of the unsaturated lactones (118) owing to Baeyer-Villiger oxidation during the H2O2 oxidation of the a-phenyl selenyl intermediate (see also ref. 210). 

If 3-chloro-N-nitrosopiperidine is used instead of the tosylate, 3,4-dehydro-N-nitrosopiperidine is formed in high yield. Another, perhaps more general, route to the vinylnitrosamines makes use of the acidity of the hydrogens on the a-carbon of nitrosamines (18). The resulting carbanion reacts smoothly with phenyl-selenyl chloride. The adduct is then oxidized with m-chloroper-benzoic acid (19). 

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