Phenylselenol

Benzeneselenol (phenylselenol, selenophenol) [645-96-5] M 157.1, b 57-59 /8mm, 71-72 /18mm, 84-86 /25mm, d 1.480, n 1.616. Dissolve in aq N NaOH, acidify with cone HCl and extract with Et20, dry over CaCl2, filter, evap on a steam bath and distil from a Claisen flask or through a short... 

In analogy to the formation of thiolesters, some selenolesters have also been synthesized from carboxylic acid, phenylselenol, and A -carbonyldi-1,2,4-triazole.tl80]... 

Selenoglycosides of sialic acid have been successfully prepared in excellent yields from the corresponding peracetylated glycosyl chloride with phenylselenol in the presence of N,N-di-isopropylethylamine [519]. This reagent combination succeeded where others were less effective or failed (Scheme 4.98 [520]. 

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]. 

Scheme 66. Reaction conditions i, LDA, CH=CCH2Br ii, LiAlH4 iii, DHP-TsOH n-BuLi-ClCOzMe TsOH-MeOH iv, EijN v, m-CPBA vi, PhCOCI-Py 1 N HCl-THF PhCOCl-Py MeON-AcCl MeONa-MeOH vii, TsCI phenylselenolate anion viii, H2O2-THF, Et3N ix, MeOH-H20-Et3N, AcjO-Py, 6-chloro-l-(p-chlorobenzenesulfonyloxy)benzotriazole-Et3N-NH3 ...

The compounds obtained by the replacement of ring sulfur by carbon, as in the case of penicillins, show somewhat improved antibiotic properties. A free radical— based route has been described for the conversion of fermentation derived cephalosporins to their carbocyclic derivatives. The first step in this sequence consists of the condensation of the cephalosporin sulfone (36-1) with formaldehyde and dimethyla-mine the initial product from the Mannich-like reaction consists of the exomethylene derivative at the position adjacent to the activating sulfone. The product is treated in situ with phenylselenol to give the Michael adduct (36-2). This fragments with an extmsion of sulfur dioxide when heated with the free radical initiator AIBN in the presence of tributyltin hydride the reaction can be envisaged as leading to the... 

The reaction of ZrCl4 with Al(SePh)3 in ether-benzene yields the phenylselenolate Zr(SePh)4 as a turquoise, microcrystalline product.499... 

Phenylselenol, diphenylphosphine and diphenylarsine cleave Pt—Me bonds, but N-bromosuccinimide and 2-nitrobenzenesulfenyl chloride oxidize the methyl platinum(II) compounds to methyl platinum(IV) complexes (equations 208 and 209).573 m-Chloroperbenzoic acid cleaves the Pt—benzyl bond in PtCl(CHDPh)(PPh3)2 with retention of configuration at carbon.574... 

Hydrogen chloride Benzoyl chloride Hydrogen Phenylselenol Pyridine Ozone... 

BF3OEt2 (0.060 ml, 0.48 mmol as a solution of 48% in BF3) and phenylselenol (0.064 ml, 0.60 mmol) were added to a stirred solution of methyl 4,6-di-O-benzoyl-2,3-dideoxy-3,3-difluoro-a-D-erythro-hexopyranoside (100 mg, 0.24 mmol) in anhydrous dichlormethane (2 ml). The solution was heated to reflux for 3 h, neutralized by dropwise addition of pyridine and evaporated to dryness. The residue was purified by column chromatography (hexane/ethyl acetate 10/1) to afford 92 mg (72%) of phenyl 4,6-di-0-benzoyl-2,3-dideoxy-3,3-difluoro-l-seleno-a-D-erythro-hexopyranoside as an anomeric mixture. 

Phenyllithium, for example, unlike benzene, reacts with ketones to form tertiary alcohols or with elemental selenium to form first phenylselenol and thereafter, through oxidation, diphenyl diselenide (Figure 5.42). 

Acyl radicals. Tributyltin hydride in combination with AIBN can generate acyl radicals from phenylselenol esters, which are a better source than acyl chlorides or phenylthiol esters for acyl radicals for intramolecular cyclization. 

A photosensitized activation of carbon-selenium bonds was also used for performing phenylseleno group transfer reactions. This process involves a photosensitized electron transfer (PET) as the initial step in the reaction sequence. Fragmentation affords a radical and phenylselenolate, which is oxidized to diphenyl diselenide in the presence of oxygen. The cyclized radical is then trapped by diphenyl diselenide to afford the final product. This process is quite general for intramolecular radical reactions.70,266... 

Diisobutylaluminum phenylselenolate (39), which is prepared in situ by the reaction between diphenyl diselenide and diisobutylaluminum hydride (DIBALH) [67], is also a useful nucleophilic selenium reagent (Scheme 37). For example, 39 reacts with oxime sulfonates to produce selenoimidic esters... 

First, small amount of impurities such as diphenyl diselenide can drastically enhance the rate of reduction by building phenylselenol in situ [3]. This can be a severe drawback, since direct reduction becomes more rapid than the desired radical reaction (usually and inter- or intramolecular carbon-carbon bond forming reaction). This effect is discussed in detail in Sect. 4.2.2. 

From alcohols. Alcohols can be transformed into phenylselenides in a stepwise manner via mesylation and reaction with lithium phenylselenolate. This procedure offers obvious advantages over the formation of the corresponding bromides or iodides when subsequent reaction with strong nucleophiles, such as organolithium compounds, are necessary to prepare the radical precursors. The diol 8 is converted to the bis(phenylselenide) 9 via the corresponding bis(mesylate) as shown in Scheme 2 [6]. Compound 9 is converted to the radical precursor 11 via reaction with lithium phenylacetylide followed by alkylation with allylbromide and a Pauson-Khand reaction. Such a reaction sequence would not be feasible with an alkyl halide. The cyclization afforded the expected tricyclic compound 12 in 95% yield. 

From lactones. Lactones can be opened with phenylselenolates in THF-HPMA. This reaction has been used to prepare a range of radical precursors as shown in Scheme 3 [8,9]. It is interesting to note that the selenide 17 furnishes the product... 

PhSeSiPh2(f-Bu) afforded a silyl radical that can abstract a bromine atom from 152 to give the radical 153. Cyclization affords radical 154, which react with diphenyl diselenide to give 155. Diphenyl diselenide results from the oxidation of the phenylselenolate anion presumably by the oxygen present in the solvent. 

A convenient synthesis of 4-methyl- and 4-phenylseleno-l,l,l-trihalo-3-alken-2-ones 74 from the reaction of the corresponding 4-methoxy-l,l,l-trihalo-3-alken-2-ones 73 with methyl- or phenylselenols in the presence of boron trifluoride etherate was reported. The reaction of 74 (R = Me) with bromine followed by ammonia led to 3-trihalomethyl-isoselenazoles in good yields (Scheme 26) <2002S2220>. 

Only very powerful soft nucleophiles like phenylselenolate and phenylthiolate ions are capable of opening monoactivated cyclopropanes (equation 38), whereas formation of a cyclopropane carboxylate has been observed with the bicyclic lactone in equation 39 . 

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