Phenylselenyl chloride

Reaction of the quinoxalinylamidine 135 with phenylselenyl chloride in aqueous triflic acid-acetonitrile gives the benzo-annulated imidazopteridine 136 <1996JHC169> (Equation 30). 

Bromination of norperistylane-5,ll-dione (835) gives rapidly and quantitatively the Cj -symmetric dibromide 836a. Similarly, reaction with phenylselenyl chloride delivers 836b . Decomposition of the bis(selenoxide) in glacial acetic acid led to diketo diacetate 837. This product enters into twofold exchange reactions with representative nucleophiles. 

Allyl alcohols readily react with trichloroacetonitrile to give the corresponding trichloroacetimidates 145. Activation of the double bond with electrophilic reagents results in ring closure to yield oxazolines 146. The most commonly employed electrophiles include iodine, iodine monochloride, phenylselenyl chloride, and mercuric trifluoroacetate. Other nitriles including cyanogen bromide and N,N-dimethylcyanamide can also be used. Since oxazolines readily hydrolyze to amides, the net effect of this reaction sequence is to produce p-amino alcohols 147 from an allyl alcohol. This strategy has been employed in numerous total syntheses of natural products. Examples are listed in Table 8.18 (Fig. 8.7 Scheme 8.43). ° ... 

The hexaruthenium dianion 4 reacts rapidly with phenylselenyl chloride (PhSeCl) in dichloromethane at room temperature to afford... 

Phenylselenyl chloride adds to the double bond of the glycal 26 to give a phenyl-selenoxonium ion which is tra/w-opened by an approaching nucleophile to the glycoside 27. Other electrophiles have also been used likep-toluenesulfonic acid, bromine, or iodine. Acid conditions, however, may cause destruction of labile 2-deoxy sugar products and the value of such reagents will be diminished by this evident disadvantage. 

The total synthesis of ( + )-Erysotramidine (2) has been described by Ito et al. (137) starting from the amide (174) (Scheme 39). After O-mesylation to 177, base-catalyzed reaction gave the cyclopropane derivative (178) which with zinc in acetic acid was reduced to 179, which was identical to the product (135) of O-methylation of 172. Conversion of 178 to the thioketal (180) was followed by reaction with phenylselenyl chloride. A mixture of two compounds, 181 and 182, was produced the former could be transformed quantitatively to the latter. Finally, treatment of 182 with silver nitrate in methanol gave 183, which was then desulfurized to yield erysotramidine (2). 

Phenylselenyl chloride adds to alkenes in a stereoselective trans manner950. The adduct is oxidized by chlorine and the seleno moiety is displaced by chloride with inversion of the configuration to yield the cis dichloro adduct (equation 142)951. 

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... 

The pure major diastereomer 138 on / -elimination gave the dihydroxythiaglycal 139, which on electrophilic glycosidation using phenylselenyl chloride and silylated nucleobase provided the major a-phenylseleno-/ -anomer 140, along with a small amount of the / -phenylseleno-a-anomer. In a similar reaction, the iodo compound was obtained when PhSeCl was replaced with AT-iodosuccinimide (NIS) (Scheme 37). 

An electrophilic cyclization of allene 98 with phenylselenyl chloride led to the formation of selenophene 99 along with dihydroselenophene 100 (Equation 14) <2004PS(179)1681>. 

Alternative reaction pathways exploring different synthetic possibilities have been studied. For instance, electron-rich dihydroazines also react with isocyanides in the presence of an electrophile, generating reactive iminium species that can then be trapped by the isocyanide. In this case, coordination of the electrophile with the isocyanide must be kinetically bypassed or reversible, to enable productive processes. Examples of this chemistry include the hydro-, halo- and seleno-carba-moylation of the DHPs 270, as well as analogous reactions of cyclic enol ethers (Scheme 42a) [223, 224]. p-Toluenesulfonic acid (as proton source), bromine and phenylselenyl chloride have reacted as electrophilic inputs, with DHPs and isocyanides to prepare the corresponding a-carbamoyl-(3-substituted tetrahydro-pyridines 272-274 (Scheme 42b). Wanner has recently, implemented a related and useful process that exploits M-silyl DHPs (275) to promote interesting MCRs. These substrates are reacted with a carboxylic acid and an isocyanide in an Ugi-Reissert-type reaction, that forms the polysubstituted tetrahydropyridines 276 with good diasteroselectivity (Scheme 42c) [225]. The mechanism involves initial protiodesilylation to form the dihydropyridinum salt S, which is then attacked by the isocyanide, en route to the final adducts. 

When phenylseleno derivatives are employed to prepare tetrahydrofurans from 4-alkenols, moderate stereoselectivity is generally observed. Cyclization of syn-(Z,Z)-7-benzyloxy-3,9-di-en-6-ol (22) with phenylselenyl chloride in dichloromethane at — 78 °C affords the corresponding 2,5-disubstituted tetrahydrofuran in 89% yield and 75 25 (trans/cis) diastereomeric ratio12. 

Total 2,3-trems selectivity is observed for the cyclization of 22 with phenylselenyl chloride in dichloromethane. The phenylseleno derivative 23 is formed as a unique diastereomer owing to the steric constriction of the isopropylidene group that biases the formation of the 23-trans-r -bose derivative28. 

Finally, it is worth mentioning that cycloetherification of alkoxy-3-alkenes, performed with phenylselenyl chloride in dichloromethane in the presence of potassium carbonate, is effective for the preparation of 2,5-cw-disubstituted tetrahydrofurans in good yield and with very high stereoselection129 136. 

Phenylselenyl chloride is also an effective electrophile in the cyclization of (Z)-5 and the corresponding glucoside 6 is obtained in 75% yield as a 20 80 (a// ) diastereomeric mixture. This stereoselectivity is opposite to that obtained by cyclization with mercury(II) trifluoroacetate94. 

Scheme 19. Cyclizations of 2-Substituted-3-alkenols into Tetrahydrofuran Derivatives Promoted by Phenylselenyl Chloride...

Jacobi extended this methodology for the synthesis of the novel sesquiterpene ( )-paniculide A (528) (Scheme 66) (84TL4859). Thermal cycloaddition of 518 in ethylbenzene in a similar condition afforded the methoxyfuran 520 in 94% yield through the intermediate 519. Phenylselenation of 520 with LDA and phenylselenyl chloride gave a 1 1 mixture of phenylselenides 521, which upon kinetic deprotonation-protonation afforded the a-isomer (522) in... 

Phenylselenyl chloride, C HjSeCI, and phenylselenyl bromide, C Hs eBr, in connection with oxidizing agents such as hydrogen peroxide or sodium periodate, are used for the conversion of aldehydes, ketones, and esters into their a,p-unsaturated analogues. The key intermediate is alkyl phenyl selenoxide, which decomposes via a five-membered transition state [167] (equation 27). 

As for the introduction of a selenium atom into carbohydrates, addition reactions to glycals are also effective. Thus, the glucal 81 can be treated with phenylselenyl chloride and gives mainly the fraws-diaxial product 153 (O Scheme 69) [112]. Similarly, azidophenylselenylation of perbenzylated glucal 104 proceeds smoothly to give 2-5 e-phenyl-2-selenoglycosylazides 154 and 155 (O Scheme 69) [113]. 

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