Phenyl selenol

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). 

Reductive elimination of 1,2-dibromoalkanes has been studied by many investigators using sodium disulfide, poly(styrylmethylthiol), methyl- or phenyl-selenolate, bis(2-thienyl)ditel-luride/NaBHj, sodium telluride/rongalite and trimethylstannylsodium. Among these, sodium sul-... 

In 1962 Renson et al. reported that a variety of selenol esters can be synthesized by the reaction of the appropriate acyl chlorides with selenols in the presence of pyridine. - Selenols can easily be prepared from elemental selenium and the corresponding Grignard reagents. In addition to simple selenol esters, a,P-unsaturated selenol esters (4) and (5) and o-substituted aromatic selenol esters (6) have been obtained by this method, as shown in Scheme 1. Butyl selenol esters are generally colorless or light yellow liquids, whereas the phenyl or substituted phenyl selenol esters are white solids, which are easily purified by recrystallization. More recently other groups have used Renson s method to synthesize similar selenol esters. " ... 

Intramolecular capture of the acyl radical formed in situ from a selenol ester and tin hydride has been examined successfully. Phenyl selenol esters (51), with an unsaturated functional group (C—C etc.) at... 

In 1980, Graf and co-workers reported that phenyl selenol esters underwent reduction to the corresponding aldehydes and alkanes (reduction and decar-bonylation) in the presence of trialkyltin hydrides and a free-radical initiator through generation of acyl radicals (Scheme 21) [97]. 

Using pyridine as solvent for Pd(OAc)2[Pg.105]

Krief and his co-workers have reported that u/c-dihalides (chlorine, bromine, iodine) and /3-halogenoselenides are converted into olefins on reaction with methyl or phenyl selenolate. Furthermore, the reductions are highly stereoselective, occurring via formal anh-elimination of the two heteroatomic moieties for dibromides e.g. Scheme 17), j8-chloroalkyl iodides, and /8-... 

Lithium phenyl selenolate, LiSePh, is sufficiently nucleophilic to add in conjugate [l,5]-fashion to monoactivated cyclopropyl ketones, nitriles, and esters/ ... 

Alkyl phenyl setenides selenol esters. N-PhcnylscIcnophthalimidc 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 l). ... 

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... 

Relatively little is known about the photochemistry of phosphorus containing organic substrates. Continuing our photochemical work on compounds of structure 1a and b which leads to thio- and selenoxanthones 3a,b via thiol ester-thiopyrone-, selenol ester-seleninone-transformations ( 1, 2, 3), or photo-Friedel-Crafts-reactions ( 3-6J, respectively, "(ScFeme 1) we have extended our interest to aroyl diphenyl phosphines 1c - k (Schemes 2-5) in which X in 1a and b stands for P-phenyl. 

Also widely employed are organoselenium compounds containing group 14 elements. Phenyl trimethylsilyl selenide 102 can be easily prepared from diphenyl diselenide 8 and is a good source for selenium nucleophiles (Scheme 24). In the presence of methanol selenols are generated for use in Michael reactions or in ring-... 

This naked selenolate is more reactive than the one complexed with borane 1 [1]. For example, in the presence of HMPA, 4 undergoes an SN2-type ester cleavage to produce the corresponding acids and alkyl phenyl selenides (Sect. 3.3) [6 a]. Uncomplexed selenolate 4 can also be prepared by the reduction of benzeneselenol (PhSeH) with sodium hydride (NaH) (Scheme 4b) [6aj. 

Selenolates prepared from diphenyl or dimethyl diselenide by reduction with NaBH4 smoothly transform various benzylic alcohols 24 into the corresponding selenides 25 in the presence of aluminum chloride (Scheme 30 a) [41]. AICI3 is considered to activate the alcohol substrate by coordinating to the oxygen. Similar transformations are possible by the reaction of alcohols with phenyl selenocyanate in the presence of tributyl phosphine [52]. When the selenolate is reacted with aromatic aldehydes or ketones 26 in the presence of AICI3, the corresponding benzylic selenides 27 are obtained in moderate yields (Scheme 30b) [41]. 

Tri(organoseleno)boranes 35 are prepared from boron trihalides and organic selenolates as stable compounds (Scheme 35) [63]. These selenoboranes have been shown to be useful for the conversion of carbonyl compounds into seleno-acetals 36 [64] and the selective ring opening of epoxides [65]. Recently, it was reported that tri(phenylseleno)borane reacts with cyclic ethers to produce m-hydroxyalkyl phenyl selenides 37 in the presence of a catalytic amount of Lewis acid [43]. 

The analogy between phenyl thiolate (Ph-S ) and ferrocenyl thiolate (Fc-S ) anions leads to the expectation that many compounds containing ferrocenyl thiolate units as either substituents or ligands should exist. This is indeed the case and, although with fewer examples, is also true for ferrocenyl selenolate and tellurolate. Similarly, l,T-ferrocenylene dithiolate compounds (which correspond to o-phenylene dithio-lates) are known, together with the analogous l,r-ferrocenylene diselenolates and ditellurolates. 

The direct selenoacetalization of carbonyl compounds by selenols is by far the shortest and most convenient route to selenoacetals. The reaction is usually carried out at 20 C with zinc chloride (0.5 equiv. versus the carbonyl con x>und) and delivers rapidly (<3 h) and in reasonably good yields methyl and phenyl selenoacetals derived from aliphatic aldehydes and ketones and cyclic ketones (Scheme 69). Selenoacetalization is more difficult to achieve with hindered ketones, such as adamantanone and diisopropyl ketone, and with hindered aromatic carbtmyl compounds. In these cases the reaction is best achieved with titanium tetrachloride instead of zinc chloride and is often limited to the methylseleno derivatives (Scheme 78). Tris(methylseleno)borane offers the advantage of not requiring an acid catalyst and is particularly useful for the selenoacetalization of acid labQe aldehydes such as citronellal (Scheme 70, e). 

Reaction of carboxylic acids with phenyl dichlorophosphate, followed by the addition of bensenesele-nol to the mixture afforded selenol esters (Scheme 4). The reaction is assumed to proceed via the penta-covalent oxyphosphorane intermediates (11a) and (11b). 

Since phenyl selenocyanate (25 Ar = Ph) is a sensitive liquid, which slowly decomposes on storage during a few days, an improved method using A -phenylselenophthalimide (A -PSP 27), a stable crystalline compound, has been developed. In general, the yields of selenol esters prepared from N-PSP/BuaP are higher than those obtained employing ArSeCN/BusP. 

Although unable to metallate selenides, dialkyl amides are sufficiently strong to metallate phenylselenoacetals39,46 51) as well as methyl48,52) and phenyl 46,47,52) selenoorthoesters. They are also able to metallate selenoxides 4 9,11 53 55) and selenones 14). Finally selenoacetals are readily available 4,711,12 S6) from carbonyl compounds and selenols in the presence of a Lewis acid and selenoorthoesters have been prepared from orthoesters, selenols, and boron trifluoride etherate47,48,52). 

Methylsulfanyl-3-(4-methylsulfanylphenyl)- (3a) and 2-methylselanyl-3-(4-methylsulfanyl-phenyl)cyclopropenone (3b) were obtained by treatment of the potassium salt of 2-(4-methyl-sulfanylphenyl)-3-oxoeycloprop-l-ene-l-thiolate and -1-selenolate with iodomethane in acetonitrile at 20 °C for 4hours. ... 

The photo-induced cyclizations of the selenol esters (20) and (21) to give (22) and (23), respectively, have been described. Photolysis of benzyl phenyl selenide (24a) or of the phenyl ribosyl derivative (24b) yield the corresponding diselenides (25). The photoreduction of acetophenone by H2Se has been investigated. ... 

Scheme 28, by application of the known thiol ester-thiopyrone phototransformation to selenium-containing systems. 5/f-[l]Benzoselenino[2,3-6]-pyridine, 4.ff-selenolo[2,3-6][l]benzoselenine, and 9/f-seleno[3,2-6][l]benzo-selenine have similarly been obtained by the corresponding selenol ester-seleninone conversion. Phenyl areneselenosulphonates undergo facile photo-induced homolysis of the selenium-sulphur bond in the presence of alkenes, a free-radical chain reaction leads to the formation of -phenylselenosulphones. ... 

The direction of the reaction of the salts of 2-phenylethynyl-selenols with acetylenecarboxylic esters has been found to depend on the nature of the cation. From the reaction of potassium 2-phenylethynylfeelenolate with dimethyl acetylenedicarboxylate, dimethyl 4-phenyl-2,3-selenophendicarboxylate was the main product.The reaction at 100-120°C of vinylacetylene with selenium in DMSO containing aqueous potassium hydroxide gave (387) as 138... 

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