Selenides, phenyl

Additionally, once the glassware has been assembled and placed under an inert atmosphere, but before the addition of any solvents or reagents, it should be flame dried using the Bunsen burner in tandem with a flow of inert gas. Care should be taken not to use a naked flame in the proximity of flammable solvents or oils. Safety glasses should be worn during this experiment and all manipulations should be performed in a fume cupboard whilst wearing protective gloves. 

The use of selenium in carbohydrate chemistry dates as far back as 1917 with the synthesis of selenoisotrehalose [35]. However, it was not until 1991 that selenoglycosides were first used as glycosyl donors [36]. It should be noted that while a wide variety of selenoglycosides are reported in the literature [37] their use as glycosyl donors has to date been confined almost exclusively to phenyl 

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AUylic phenyl selenides are obtained by the reaction of allylic acetates with diphenyldiselenide and Sml2[233]. 

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). 

Trifluoromethyl thiirane is formed by the action of tris(diethylamino)-phosphineon l-chloromethyl-2,2,2-trifluoroethyldisulfide [S2] (equation 73) Difluoromethyl phenyl selenide is prepared by treatment of lithium phenyl-selemde with chlorodifluoroniethane via a carbene mechanism [Si] (equation 44) Bis(2,2,2-trifluoroethyl)diselenide is formed in the reaction of 2,2,2-trifluoroethyl mesylate with lithium diselenide [84] (equation 74). 

Primare Alkohole konnen leicht fiber Phenyl-selenide durch Reduktion mit Triphenyl-zinnhydrid in Kohlen-wasserstoffe Ubergeffihrt werden6. 

The number of reported reactions in which the radical derived from the decomposition of AIBN plays a role in the termination process has increased considerably. Often these reactions are not radical chain reactions, since the initiator is used in stoichiometric amounts. A few examples of rearomatization of cyclohexadienyl radicals by disproportionation have been reported herein. Below are some other examples, where the phenyl selenide 61 reacts with (TMSfsSiH (3 equiv), AIBN (1.2 equiv) in refluxing benzene for 24 h to give the coupling product of radicals 63 and 64 in good yields (Scheme 9).i24,i25 these cases,... 

Diphenyl diselenide has been prepared by disproportionation of phenyl selenocyanate in the presence of potassium hydroxide" or ammonia/ and by air oxidation of benzeneselenol. The preparation of benzeneselenol is described in an earlier volume in this series/ In the present procedure phenylselenomagnesium bromide formed from phenylmagnesium bromide and selenium is oxidized directly to diphenyl diselenide with bromine/ Thus the liberation of the malodorous and toxic hydrogen selenide and benzeneselenol is avoided. Benzeneselenenyl chloride has been prepared by thermal elimination of ethyl chloride from ethyl phenyl selenide di-chloride/ by thermal elimination of chlorine from phenylselenium trichloride," and by chlorinolysis of diphenyl diselenide with either sulfuryl chloride " or chlorine. " ... 

Ethyl phenyl selenide dichloride Selenium, dichloroethylphenyl-... 

The submitter has synthesized nine alkyl phenyl selenides in yields of 85-95% by treating alcohol solutions of the sodium salt (the selenophenol is dissolved in the calculated amount of 50% aqueous sodium hydroxide diluted with alcohol) with the appropriate alkyl halide or sulfate. 

As has been described for allyl bromide (see preceding paragraph), allyl sulfides and allyl phenyl selenide react with 6-diazopenicillanates 134 under Cu(acac)2 catalysis to give the products of ylide formation and subsequent [2,3] rearrangement 155-159). Both C-6 epimers are formed. The yields are better than with BF3 Et20 catalysis, and, in contrast to the Lewis acid case, no 6[Pg.139]

Tetraalkylammonium borohydrides react with elemental selenium and tellurium to form the symmetrical dialkyl selenides and tellurides [44]. Diphenyl selenide yields the alkyl phenyl selenides. 

Table 12 Oxidation potentials of alkyl phenyl selenides...

In a range of anions PhZ (Z = O, S, Se, Te), for example, the thiophenolate ion (PhS ) effectively traps aryl radicals (Ar ), whereas the anion of phenyl selenide (PhSe ) is 20 times less active, and the phenolate anion (PhO ) is absolutely inactive. The reaction of aryl radicals with phenyl-telluride ions (PhTe ) proceeds in an abnormal fashion—both asymmetrical and symmetrical tellurides are produced (Rossi and Pierini 1980). 

T(—H) can also be formed in a two-step process involving radical cation formation produced by photosensitizers operating through a type I mechanism, followed by deprotonation. Cadet has also developed the photolabile phenyl sulfide precursor that upon irradiation at 254nm generates T(—H). " The corresponding phenyl selenide" and methoxy-substituted sulfides" were developed by the Greenberg... 

Transfer of a metal carbene moiety from a metal carbene complex to a heteroatom other than oxygen, sulfur, and nitrogen is possible. One such example is the report by Uemura and co-workers, who disclosed catalytic asymmetric reaction of ethyl diazoacetate with ( )-cinnamyl phenyl selenide 193 (Equation (30))." The reaction afforded 194 as a diastereomeric mixture (58 42). Using Rh2(5[Pg.173]

Formation of CK-configurated cyclobutanones has also been observed with 2-methylcyclopen-tanone and 2-methylcyclohexanone/8 However, stereoreversed eyclobutanone formation can be achieved by opening the intermediate oxaspiropentane with sodium phenyl selenide, oxidation of the resulting / -hydroxy selenide with 3-chloroperoxybenzoic acid and subsequent rearrangement in the presence of pyridine/18 Thus, from one oxaspiropentane 8, either stereoisomeric eyclobutanone cis- or lrans-9 was produced. The stereoreversed eyclobutanone formation proceeds from a stereohomogenous / -hydroxy selenoxide and is thought to be conformationally controlled. 

Alternatively addition of lithiomethyl phenyl selenide to cyclobutanones followed by treatment with iodomethane and base is reported to yield the spiroepoxide.222... 

Utilizing selenoxide syn elimination as the key step, a two-step procedure has been developed for the conversion of ketones to enones.22 Cyclobutyl phenyl ketone (52) and 3-phenylcyclobu-tanone (55) were both transformed via the phenyl selenides to the corresponding 1-cyclobutenyl phenyl ketone and 3-phenyIcyclobut-2-en-l-one in 74 and 26% overall yield, respectively.22... 

OH - Br. A primary or secondary alcohol can be converted to the alkyl phenyl selenide by reaction with phenyl selenocyanate and tri-n-butylphosphine (7, 252-253). Reaction with Br2 and triethylamine (7, 34-35) replaces the SeC6H5 group by Br. 

Phenyl selenides.2 In the presence of a ruthenium catalyst, prepared by reaction of RuCly with 3 equivalents of potassium, lithium benzencselenolate reacts with a wide variety of tertiary amines to form phenyl selenides in excellent yield. Anhydrous diglyme is used as solvent. 

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). ... 

Atkenes from sic-dihaiides. The reaction of /c-dihalides with NaSeCH3 or NaSeC6H5 in ethanol or THF-HMPT (3 1) results in alkenes. The reaction involves a formal a rr-elimination in the case of wc-dibromides or uie-chloroiodidcs, but a formal xyn-elimination in the case of w c-dichlorides. Elimination to form alkenes also occurs with /K-haloalkyl phenyl selenides. 

Synthesis of alkenes. Terminal alkenes are formed in good yield by oxidation of primary alkyl 2-pyridyl selenides with a slight excess of H202 (equation I). The same reaction with primary alkyl phenyl selenides proceeds in much lower yield. 

The treatment of furfuryl phenyl selenides (178) with n-butyllithium or metallic lithium affords furfuryllithium reagents which undergo ring opening to furnish initially the allenic ketones (180) (80TL3209). Two equivalents of n-butyllithium are required for complete conversion due to the acidic character of the allenic hydrogen. The allenic ketones are readily isomerized to the dienones (181) on p-toluenesulfonic acid treatment (Scheme 38). 

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