Phenylseleno-1-alkenes

Deprotonation. Organolithium species are obtained from l-alkoxy-3-phenylseleno-1-alkenes (subsequent regioselective alkylation occurs at C-3), selenoamides, and selenono-thioesters. When those derived from oi,p-unsaturated acids condense with nitriles 2-pyridones are obtained. ... 

C in the dark, providing vicinal bis(phenylseleno)alkenes in good yields... 

Se-phenyl areneselenosulfonates (24) undergo facile free-radical addition to alkenes to produce / -phenylseleno sulfones (25) in excellent yield86,87 (see Scheme 7). The addition occurs regiospecifically and affords anti-Markovnikov products contrary to the analogous boron trifluoride catalyzed reaction which produces exclusively Markovnikov and highly stereospecific products86 (equation 37). Reaction 36 has been shown to have the radical... 

Phenylseleno derivatives 71 are found to be good precursors of phosphonodi-fluoromethyl and phosphonothiodifluoromethyl radicals (Scheme 11). Moreover, when generated by the (TMS)3Si attack on 71 and in the presence of alkenes or... 

The (TMS)3SiH mediated addition of phosphorus-centered radicals to a number of alkenes has been investigated in some detail. Reaction (73) is an example of phosphorous-carbon bond formation using four structurally different phenylseleno derivatives with 3 equiv of (TMSlsSiH and AIBN in refluxing benzene for 2h. Comparative studies on the reaction of the four phosphorus-centered radicals have been obtained. Although the reaction with 1-methylene cyclohexane is efficient with all four derivatives, different selectivity is observed with electron-rich or electron-poor alkenes. 

Acyl radicals can be generated and they cyclize in the usual manner. A polyene-cyclization reaction generated four rings, initiating the sequence by treatment of a phenylseleno ester with Bu3SnH/AIBN to form the acyl radical, which added to the first alkene unit. The newly formed carbon radical added to the next alkene, and so on. Acyl radicals generated firom Ts(R)NCOSePh derivatives cyclize to form lactams. ... 

The Homer - Emmons reagent (52) is effective in the one carbon homologation of ketones possessing acidic a-hydrogen atoms <96SL875> and electron-deficient alkenes add to 2-phenylseleno-l,3-dithiane in a photo-initiated heteroatom stabilised radical atom transfer process, giving products of considerable synthetic potential <96TL2743>. 

Activation of alkenes towards nucleophilic attack by a variety of nucleophiles employing A-phenylselenophthalimide or A-phenylselenosuccinimide as an electrophilic source of the phenylseleno group. 

Bei einer Variante dieser Reaktion erhalt man N-geschiitzte primare Allylamine, indem man das l-Phenylseleno-2-alken in Methanol mit Chloramin-T oder mit Carbamid-saure-benzylester/N-Chlor-succinimid/Triethylamin umsetzt2,4, wie hier fur die Herstel-lung von 3-Methyl-3-(4-methyl-henzolsulfonylamino)-l-buten (88%) und (2R,3E)-4-(Be-nzyloxycarbonyl-amino)-2-penten (56%) formuliert. 

Alkenes from p-oxygenated selenidesS /J-Phenylseleno lactones, ethers, and alcohols are converted into alkenes on treatment with ClSi(CHj)j and Nal in C HiCN. Hydriodic acid (formed by inadvertent hydrolysis) may play a role this acid cun effect this reaction, but in lower yield. This elimination thus reverses cyclo-(unclionali/ations induced by C6H5ScX (cf Na-NH3, 9, 26), and in addition provides a stereospecific route to alkenes by way of/l-hydroxv selenides. lixnmplc ... 

Cleavage of epoxides. Tris(phenylseleno)borane and tris(meChylseleno)borane2 react rapidly with terminal and a,/ -disubstitutcd epoxides to give /1-hydroxy selenidcs, or in some cases alkenes. In the latter case, there are marked differences between the cis- and frans-cpoxidcs the latter react very slowly to give mainly trans-alkenes. 

Reductive coupling of carbonyls to alkenes Titanium(IV) chloride-Zinc, 310 of carbonyls to pinacols Titanium(III) chloride, 302 Titanium(IV) chloride-Zinc, 310 of other substrates Samarium(II) iodide, 270 Reductive cyclization 2-(Phenylseleno)acrylonitrile, 244 Tributylgermane, 313 Tributyltin hydride, 316 Triphenyltin hydride, 335 Trityl perchlorate, 339 Reductive hydrolysis (see Hydrolysis) Reductive silylation Chlorotrimethylsilane-Zinc, 82... 

The formation of bicyclo compounds by the radical cyclization of alkenes with strategically placed phenylseleno groups, promoted by Bu3SnH, occurs in high yields and gives... 

Trimethylsilyl-1,3-bis-(phenylseleno)propene, 60 Trimethylsilyl-5-chloro-l, 4-dienes, 49 Trimethylsilyldiazomethane, 573-574 2-Tnmethylsilylethanol, 4, 574 P (Trimethylsilyl)ethyllithium, 574-575 2-Trimethylsilylfuranes, 577 3 -Tnmethylsiiyl-4-hydroxy-1 -alkenes, 175 N-(TrimethyIsilyl)imidazole, 575 Trimethylsilyllithinm, 575 Trimethylsilylmethanethiol, 576 1 -Trimethylsilyl-1 -methoxyallene, 577 2-(Trimethylsilylmethyl)-3-acetoxy-1 -propene, 578-579... 

Photoaddition to alkenes. On irradiation 1 dissociates to C6H5Se and C6HsS02 irradiation in the presence of an alkene initiates a chain reaction leading to p-phenylseleno sulfones in good yield. 

Acyl radicals from RCOSeCfH. Acyl radicals generated from phenylseleno-esters can participate in inter- and intramolecular alkene addition. The latter tandem... 

Another useful reaction for the difunctionalization of olefins involves a group transfer carbonylation starting from a a-(phenylseleno)carbonyl (or related derivatives) and a terminal alkene under 80 atm of CO. An alkyl radical is first formed by the photocleavage of a C-SePh bond. The addition of this radical to the olefin, followed by the incorporation of CO and radical coupling with PhSe-, gave substituted selenoesters via a three-component coupling reaction [74], The intermolecular formation of C—C bonds via phenylseleno group transfer has been likewise adopted in the reaction between ester-substituted O,Se-acetals and an olefin [75],... 

The radical addition of selenomalonate 149 or the corresponding malononitriles are excellent substrates for phenylseleno group transfer reactions to alkenes and alkynes.263 Malononitrile 150 can be used for annulation and cyclization reactions (Scheme 40) 264,265... 

The reaction of enamines and imines with acrylamide results in aza-annulation120,121. Other electrophilic alkenes which have been used to alkylate enamines and the products used in hetero- or carbocyclic synthesis include ethyl / -nitroacrylate122, where reaction occurs beta to the nitro not the ester group, 2-(phenylseleno)prop-2-enenitrile [CH2 = C(SePh)CN]123,124, phenyl a-phenylselenovinyl sulphone [CH2 = C(SePh)-S02Ph]124 and phenyl a-bromovinyl sulphone124. An electrophilic allene, phenylsulpho-nylpropadiene, has also been used to alkylate enamines125 (Scheme 44). 

A method for the conversion of alkenes to a-phenylseleno carbonyl conqmunds involves the use of benzeneselenenic anhydride. This reagent, which has a relatively short lifetime, is prepared in situ from diphenyl diselenide and r-butyl hydroperoxide. The alkene is converted to a phmylseleniranium ion... 

The addition of phenylselenenyl chloride to a-substituted styrenes in methanol is stereoselective and gives the product of anti addition of the phenylseleno and methoxy groups to the double bond. The (E)-alkcnc gives the (/ , S )-products while (Z)-alkenes give (S, S )-products28. 

The reaction is also fully stereoselective when cyclohexene is the cyclic alkene and ethanol or 2-propanol is the solvent. ( )-2-Butene in methanol gives 2-methoxy-3-(phenylseleno)butane 24 in 82% yield containing more than 95% of the (25, 3.R )-isomer (by GC and 13C NMR). Similarly, the product obtained from (Z)-2-butene consists of more than 95% of the (25, 35 )-selenide34. 

The stereoselective formation of /3-hydroxy selenides has also been reported 36 in the reaction of alkenes with, V-(phenylseleno)phthalimide or the succinimide derivative in aqueous acetonitrile or dichloromethane. The use of phenylselenenyl chloride under these conditions gives similar results (Table 5)37. 

Table 5. 2-(Phenylselcno)cycloalkanols or /8-(Phenylseleno)alkanols from Cyclo-alkencs or Alkenes and jV-(Phenylseleno)phthalimide or -succinimide or Phenylselenenyl Chloride36-38...

A less expensive procedure that does not require the use of a silver salt involves treatment of the alkene with phenylselenenyl bromide in acetic acid43. The formation of trans-l-acetoxy-2-(phenylseleno)cyclohexane (trans-33) best exemplifies this approach. 

Effective aminoselenenylation of alkenes occurs on treatment with iV-(phenylseleno)phthal-imide (A -PSP) and cyanamide in the presence of 4-methylbenzenesulfonic acid (see overleaf)61. 

Similarly, the reaction of alkenes with phenylselenenyl chloride and a carbamate in the presence of silver tetrafluoroborate affords /5-phenylseleno carbamates62. 

Cyclohexene is converted to tnmv-1-(4-mcthylphcnylsulfonylamino)-2-(phenylseleno)cyclohexane (59) by treatment with diphenyl diselenide and chloramine-T, followed by reductive workup with sodium borohydride66. The intermediate product A formed from diselenide and chlor-amine-T is believed to play the role of an electrophile attacking the alkene. 

Addition of. Sh-phenyl 4-methylphenylselenosulfonate to alkenes can be performed in the presence of boron trifluoride-diethyl ether complex or, alternatively, can be thermally induced (Table 11)69. The boron trifluoride-diethyl ether procedure affords tram-l-arylsulfonyl-2-(phenylseleno)alkanes stereoselectively, however, the thermally induced procedure, when applied to ( )- and (Z)-l-phenyl-l-propene, is a nonstereoselective process when indene is used as the alkene it gives the tram-adduct as the major product. 

Phenylseleno thiocyanate rapidly undergoes addition to alkenes without the presence of a catalyst, producing -thiocyanates and/or /1-isothiocyanates. The stereoselectivity of the addition is less predictable than with other selenenyl electrophiles. 

In the presence of phenylselenenyl chloride and anhydrous zinc(II) chloride as catalyst, 4-toluene-sulfonyl amide added to alkenes giving iV-[2-(phenylseleno)alkyl]-4-toluenesulfonylamides 4 in good yield. The reaction proceeded with total diastereoselectivity (anti addition) and the configuration of the products was assigned by 14 NMR175. 

The stereochemical outcome of the reaction was determined using (Z)- and ( )-2-butenes as alkene substrates, syn- or n ti-2-Acetylamino-3-(phenylseleno)butane 11 was obtained starting from (Z)- or ( )-2-butene, respectively. These products are easily distinguished by their H-NMR spectra and the configuration was confirmed by comparison with an authentic sample. 

Cyanamide undergoes smooth addition to alkenes at 25 °C in the presence of A -phenylselenoph-thalimide (7V-PSP) and sulfonic acid as the catalyst, to produce /J-phenylseleno cyanamides in good yield, despite the long reaction times needed, anti- and. mi-Diastereomers 2, obtained from ( )- and (Z)-2-decene, respectively, are clearly distinguished on the basis of their H- and 13C-NMR spectra66. 

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