Selenides selenols

Keywoids Radicals, Group transfer reactions. Photoelectron transfers, Selenosulfonation, Acyl radicals, Azidoselenenylation, Selenides, Selenol... 

Ni and Se is observed in the structure of the mixed selenide/selenolate cluster [Ni2oSei2(SeMe)io] (7, Figure 13.5) [29]. The cluster contains a Ni2oSei2 core that is stabilized by surface Me groups bonded to Se centers. The interstitial selenide ligands (Se ) arise from Se-C bond scission reactions of the MeSe reagent. 

Alkyl phenyl selenides selenol esters. N-Phenylselenophthalimide is superior to aryl selenocyanates for conversion of alcohols to alkyl phenyl selenides (6, 252-253) and of carboxylic acids to selenol esters (7, 396-397). When conducted in the presence of an amine the latter reaction provides amides in high yield (equation I).2... 

The 7 a-bromo steroid (9) can also be treated with sodium phenyl selenolate (41). The resultant 7 P-phenyl selenide (13) can be oxidized and the corresponding phenyl selenoxide elirninated to form the 7-dehydtocholesteryl ester (11). 

Synthesis of thiols, selenols, sulfides, selenides, sulfoxides, sulfones, and se-lenones of heterocyclic series 98JCS(P1)1973, 99JCS(P1)641. 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

Unfortunately, the appeal of solid phase extractions on small scale fades as the scale increases due to the cost and inconvenience of using large amounts of fluorous silica gel. Here, modified techniques to reduce the tedium of repeated extractions are attractive. For example, Crich has recently introduced the minimally fluorous selenide C6Fi3CH2CH2C6H4SeH[171. This selenol is added in catalytic quantities to tin hydride reductions of reactive aryl and vinyl radicals. The high reducing capacity of the aryl selenide suppresses undesired reactions of product radicals without suppressing the reactions of the aryl and vinyl radicals themselves. After the reaction is complete, the selenol can be recovered by a modified continuous extraction procedure. 

Example 2, in addition to oxyselenide formation, carbo- and heteroseleno cycliza-tion, A -PSP can be used to generate selenides from alcohols and selenol esters from carboxylic acids, respectively, in the presence of a stoichiometric amount of n-Bu,P. ... 

In a further line of experiments lithium alkynyl selenolate, instead of acetylenic selenides, has been used to generate the zirconated vinylselenides, precursors of (E)-telluro(seleno)ketene acetals. ... 

The above-described procedure is advantageous towards the precedent method since (a) the starting lithium alkynyl selenolate is prepared in situ, avoiding the laborious preparation of the acetylenic selenides and (b) the hydrozirconation step is regio- and stereoselective, in contrast with the previously discussed hydrozirconation of acetylenic selenides resulting in a mixtnre of the regioisomers, and requires only 1 equiv of the Schwartz reagent instead of 2 eqniv of the precedent procednre. 

Oxidation of an a-silyl selenide with hydrogen peroxide leads to an aldehyde, silanol and selenol as the primary products [253]. Evidently, the fragmentation proceeds only after contrapolarization at Se, the intermediate now having an a-d-a array. 

As the rate of cyclization becomes slower, the reactivity of the precursor becomes more important. To ensure that the radical generation step does not break the chain, it is important to use the most reactive precursor available. For very slow cyclizations, the advice is simple use iodides whenever possible. The purity of the precursor is also critical for slow cyclizations because tin hydride can sometimes react with impurities to generate hydrogen atom sources that are much more reactive than itself. Any impurities that might generate thiols or selenols may cause undue amounts of reduction (thus, the purity of phenyl sulfides and selenides is especially important). Metal impurities, which may form transition metal hydrides, can be devastating, even for fast cyclizations.41 Empirically, it seems that breaking of the chain is less of... 

In the presence of /9-cyclodextrin, that binds to the R group of substituted epoxides, benzeneselenol reacts regio- and stereo-specifically to give an 80% yield of the j3-hydroxy selenide.42 Because the selenol only attacks the least substituted carbon with inversion of configuration, the reaction must occur by an SN2 mechanism. 

Alternatively polymer-bound sodium selenide 6 served as the starting point for an acylat-ing protocol (Scheme 3) [12]. Transformation into selenol ester 9 afforded an active polymer-bound intermediate which was cleaved in the presence of an alkinylcopper species to generate a,/ -alkinyl ketones 10 while the copper selenide can be reacylated using acyl chlorides. 

R-SeH R1-Se-R2 R-Se-CN Selenol Selenide Selenocyanate R1, SeR3 K SeR3 Selenoacetal... 

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