Selenides, alkyl phenyl

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. 

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...

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. 

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). ... 

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 selenoxide elimination of primary alkyl 2-pyridyl selenides to give terminal alkcnes also proceeds in higher yield than the corresponding reaction with alkyl phenyl selenides.2 Example ... 

M-1 s-1 alkyl phenyl selenides, aryl bromides, vinyl bromides, a-chloro esters, a-thiophenyl esters 104-102M 1 s-1 alkyl chlorides, alkyl phenyl sulfides, a-chloro and a-thiophenyl ethers. 

Alkylene bromide, 20, 24 Alkylene thioureas, 26, 35 Alkylidenecyanoacetic esters, 25, 48 Alkyl lactate, 26, 6 Alkyl phenyl selenides, 24, 91 S-Alkylthiuronium halides, 22, 60 d/-ALLOTHREONINE, 20, 104 Alloxan, 23, 3... 

Trialkylboranes were converted into alkyl phenyl selenides and alkyl phenyl tellurides by reactions with PhSeSePh and PhTeTePh in the presence of stoichiometric amounts of air.550 Vinyl selenides and tellurides were synthesized by treating vinylboronic acids or esters with phenylselenyl chloride in ionic liquids (Equation (114))551 or by palladium-catalyzed coupling reaction of diorgano ditellurides (Equation (115)).552... 

Although phenylsenenyl radicals can be generated easily by irradiation of diphenyl diselenide, their low reactivity toward unactivated alkenes and alkynes has prevented their extensive use in synthesis.267,268 But diphenyl diselenide can be used as an efficient trap for alkyl radicals. The products are alkyl phenyl selenides. This trapping reaction has found application to different radical reactions and the selenides obtained by this reaction can be used in subsequent reactions. 

The /V-phenylselenophthalimide (NPSP)-tributylphosphine (Bu3P) system is also a useful reagent for the facile transformation of carboxylic acids into seleno esters, and of alcohols into alkyl phenyl selenides (including some carbohydrate derivatives).102 The utility of iV-phenylselenophthalimide (N-PSP) as a selenylating agent has been reviewed by Nicolaou and co-workers.103... 

RSeCJIi — ROCHi. Oxidation of an alkyl phenyl selenide with m-chloroperben-zoic acid (2-5 equiv.) in methanol affords the corresponding alkyl methyl ethers in high yield. Oxidation of selenides with a vicinal phenyl group is accompanied by rearrangement of the phenyl group. vtc-Methoxy selenides derived from cycloalkenes are oxidized under these conditions to dimethyl acetals of ring-contracted aldehydes. 

Oxidation of alkyl phenyl selenides with excess MCPBA in alcohols results in a facile substitution of a selenone moiety by an alkoxy group (Scheme The intermediate addition compound (47) be-... 

Phenylseleneny lotion of acetates and lactones. In the presence of zinc iodide, 1 reacts with alkyl acetates to form alkyl phenyl selenides. The reaction is particularly facile with acetates of tertiary, ailylic, and benzylic aicohols. Acetates of primary and secondary alcohols react only at 110°. 

Dealkylation of amines. Most amines (primary, secondary, and tertiary) form crystalline salts with benzeneselenol. When heated (150°) some of these salts decompose to form the dealkylated amine and an alkyl phenyl selenide. Salts of primary alkylamines for unknown reasons undergo dealkylation very slowly hindered, tertiary amines are dealkylated most rapidly. 

The first example of the use of the catalytic one-pot procedure described above, in which the deselenenylation occurs with substitution, is represented by the conversion of vinyl halides into a-alkoxy acetals [116]. This is illustrated in Scheme 38 in the case of -bromostyrene 235. The regioselective methoxy-selenenylation affords the a-bromo selenide 236, which undergoes a rapid solvolysis, through a selenium-stabilized carbocation to produce the selenide 237. Oxidation of this alkyl phenyl selenide with ammonium persulfate produces an oxygen stabilized carbocation, which affords the final product 238, and, at the same time, regenerates the selenenylating agent. 

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. 

Diphenyl diselenide reacts efficiently with alkyl radicals to give alkyl phenyl selenides. The rate of this reaction for primary alkyl radicals is 2.6 x 10 M s at 25 °C. The trapping reaction could be applied to many different types of radical reactions and deliver a selenide which is particularly suitable for further functionalization of the final product. Some typical examples are presented below. 

In the former case, almost complete stereoselective oxidation to the chiral selenoxides has been accomplished quite recently. The Davis oxidant, 3,3-di-chloro-l,7,7-trimethyl-2 -(phenylsulfonyl)spirobicyclol2.2.11heptane-2,3 -oxa-ziridine, was found to be the most efficient reagent for the enantioselective oxidation of a variety of prochiral alkyl aryl selenides [81. Asymmetric oxidation was accomplished by the treatment of the selenides with 1 molar equivalent of the Davis oxidant at 0°C to afford the corresponding chiral alkyl aryl selenoxides in quantitative yields with 91-95% ee (Scheme 1). The oxidation of methyl phenyl selenide was complete within 1 min, whereas that of triiso-propyl(a bulkier alkyl) phenyl selenide required a few hours. Typical results are... 

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