8-Phenylselenyl alcohols

This ether was prepared from an alcohol and 2-(phenylselenyl)ethyl bromide (AgN03, CH3CN, 20°, 10-15 min, 80-90% yield) it is cleaved by oxidation (H2O2, 1 h ozone or NaI04), followed by acidic hydrolysis of the intermediate vinyl ether (dil. HCl, 65-70% yield). ... 

One of royal jelly acids (10-hydroxy-2-decenoic acid) (141) was prepared from the telomer of acetoacetate, 142 (128). The terminal double bond was converted to terminal alcohol by hydroboration. The internal double bond was reduced and then reintroduced at the conjugated position by the addition of phenylselenyl group, and its oxidative removal completed the synthesis ... 

Oxidation of the 7/3-phenylselenyl-A -steroids (135) with H2O2 gave the two configurationally stable R- and 5-selenoxides (136) and (137) respectively which react by independent pathways. The R-isomer (136) underwent the familiar 2,3-sigmatropic shift leading, after solvolysis, to the allylic alcohol (138) whereas the 5-isomer (137) gave the A -diene owing to pronounced steric hindrance to the... 

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). ° ... 

C is-fused tetrahydrofurans are produced when 2-cycloalkenyl-substituted ethanol derivatives are cy-clized via 5-exo ring closure (equation 14 and Table 5). The related 1-cycloalkenyl alcohol systems also yield cri-fused tetrahydrofurans upon reaction with phenylselenyl reagents, similar to their carboxylic acid analogs (see equation 12).60 A sulfoetherification to a fused ring tetrahydrofuran from a system with an exocyclic methylene provided an 86 14 ratio of cis- and frans-fused isomers.61... 

The cyclohexene 121, which was readily accessible from the Diels-Alder reaction of methyl hexa-3,5-dienoate and 3,4-methylenedioxy-(3-nitrostyrene (108), served as the starting point for another formal total synthesis of ( )-lycorine (1) (Scheme 11) (113). In the event dissolving metal reduction of 121 with zinc followed by reduction of the intermediate cyclic hydroxamic acid with lithium diethoxyaluminum hydride provided the secondary amine 122. Transformation of 122 to the tetracyclic lactam 123 was achieved by sequential treatment with ethyl chloroformate and Bischler-Napieralski cyclization of the resulting carbamate with phosphorus oxychloride. Since attempts to effect cleanly the direct allylic oxidation of 123 to provide an intermediate suitable for subsequent elaboration to ( )-lycorine (1) were unsuccessful, a stepwise protocol was devised. Namely, addition of phenylselenyl bromide to 123 in acetic acid followed by hydrolysis of the intermediate acetates gave a mixture of two hydroxy se-lenides. Oxidative elimination of phenylselenous acid from the minor product afforded the allylic alcohol 124, whereas the major hydroxy selenide was resistant to oxidation and elimination. When 124 was treated with a small amount of acetic anhydride and sulfuric acid in acetic acid, the main product was the rearranged acetate 67, which had been previously converted to ( )-lycorine (108). 

This reaction was followed by a reductive epoxide cleavage the authors had developed 216). Sodium phenylselenyl triethoxyboronate in acidic methanol cleaved the epoxide within 5 min in high yield. The resulting tertiary alcohol 409 was once more simultaneously protected with the isopropenyl double bond as... 

Consecutive treatment of an allylic stannane with SnCl4 and hexanal derivative provided the corresponding homoallyhc alcohol. Subsequent cyclization of this alcohol, promoted by phenylselenyl chloride and tin chloride, followed by reduction with Bu.Sri 11 afforded a disubstituted tetrahydrofuran as a single stereoisomer. Repetition of this procedure enabled access to pamamycin 607 which has three 2,5-cis-disubstituted tetrahydropyran moieties (Scheme 12.19) [54]. 

Photoinduced activation by electron transfer between aromatic compounds and the phenylselenyl group of selenoglycosides generates glycosyl cations that react with various alcohols to give O-glycosides.232... 

The [3,3] siginatropic shift itself proceeds with high stereoselectivity. Mixed ketene acetals can also be generated from vinyl ethers and allylic alcohols in the presence of phenylselenyl bromide157. 

Scheme 9 Santonin (41) was converted to the derivative (99), whose conversion to alcohol (100) by metal hydride reduction and Mitsunobu reaction. Diol (102), prepared from (100), on acid catalysed cyclization and followed by subjection to Mitsunobu reaction, gave (104), which was converted to ketone (106), whose transformation to homoallylic alcohol (108), was achieved by standard organic reactions. Phenylselenylation afforded (110), which was finally converted to phytuberin.

The electrophilic addition of arylbis(arylthio)sulfonium salts to glycals in the presence of alcohols, directly provide 2-thio-(5-glycosides with good stereoselectivity [162]. Stereoselective syntheses of [5-glycosides were also obtained from the reaction of 1,2-trans acetoxysele-nides, prepared by treatment of glycals with phenylselenyl chloride and silver acetate, in the presence of trimethylsilyl triflate [163]. Combined application of this method and the trichlo-roacetimidate method (see section 3.3) was suggested for the synthesis of functionalized precursors of the olivomycin C-D-E trisaccharide [164] (Scheme 34). 

The r-phenylselenyl derivative 73 was obtained, but with only low dia-stereoselectivity, by reaction of the enolate with PhSeCl. Treatment of 73 with NaBH4 in the presence of CeCh gave stereoselective reduction to alcohol 74. ... 

Phenylselenoenones can be prepared from allylic alcohols by oxidation with benzeneseleninic anhydride " or from enones by treatment with phenylselenyl... 

Allyl silanes have been found to undergo a phenylselenodesilylation sequence that places the phenylselenyl group at the least substituted terminus of the allylic system (Scheme 15), whereas phenylthiodesilylation usually occurs regio-specifically at the y-position oxidation of the allyl selenide and [2,3]-sigmatropic rearrangement of the selenoxide to a selenenate, that is trapped in situ, completes a sequence that provides allylic alcohols at the more substituted allyl terminus. 

The addition of PhSeCF2TMS to carbohydrate-derived a-chiral aldehydes provided the corresponding difluoro(phenylselenyl)-methyl adducts with acceptable diastereoselectivities (eqs 9-15). Tetramethylammonium fluoride (TMAF) appeared as the appropriate mediator for these reactions (eqs 9-13 and eq 15). The benzoyl-protected aldehyde required the use of tetrabutylammo-nium difluorotriphenylsilicate (THAT) as a mediator to give the addition product only in low yield (eq 14). The two-step procedure (the addition of TBAF in the second step) was used to convert the OH/OTMS mixture initially obtained to the free alcohols (eqs 9 and 13-15). For benzyl- and MOM-protected aldehydes, a warm-up to room temperature was sufficient to afford alcohols in high yields (eqs 10-12). 

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