Vinyl-silver intermediate

The silver(I)-catalysed 5(Q-exo-dig cycloisomerization of alkynyl silyl enol ethers, such as (267), has been reported to produce the spiro-cyclic derivatives (268). Trapping the vinyl silver intermediate with NIS afforded the alkenyl iodides (269). ... 

According to DFT calculations, the silver(I)-catalysed conversion of the prolinol-derived propargylic amine (270) into (-)-allene (273), proceeds via an initial silver(I) coordination to the C=C bond in an anft-manner with respect to nitrogen (271). The latter complex then undergoes a rate-limiting hydride transfer from the prolinol moiety (with AG =44.8 kJ mol ) to generate the vinyl-silver intermediate (272), which then affords the final allene (273) via an anri-periplanar elimination. 

Study on this allene hydroarylation reaction, the presence of dinuclear gold-gold and gold-silver intermediates was suggested (Scheme 18.19), together with vinyl gold complex, in the gold(I)-catalyzed hydroarylation [18],... 

I - Alkyny lphenyl selenides. Benzeneselenenyl bromide and silver nitrite (1 equiv.) rcncl to form a reagent (presumably C6H5SeN02) that converts 1-alkynes into 1-nlkynyl phenyl selenides (equation I).1 The same reaction has been effected in generally lower yields with phenyl selenocyanate catalyzed by Cu(I).2 The products tire useful intermediates for regio- and stereoselective synthesis of vinyl selenides. 

The highest yields for this reaction were obtained with an unsubstituted amide and with one containing a p-chloro substituent, with vinyl methyl ketone as the alkene. Use of styrene led to lower yields. The reaction of the intermediate aceta-nilidopalladacycle with methyl iodide, which produces N-o-tolylacetamide is interesting mechanistically [7b], Stoichiometrically, full conversion was achieved, but attempts with catalysts gave only 10 turnovers and required the use of silver acetate to convert palladium iodide into the acetate, because palladium iodide does not have enough activity for metalation. 

In many instances, however, solvolysis of a halocyclopropane is deliberately accomplished in order to install an essential vinyl halide or hindered olefin. In 2000, Murphy and coworkers performed a silver ion-mediated ring expansion of gem-dibromocyclopropane 18 in wet acetone to afford the allylic alcohol 19 in 82% yield (Scheme 4.5).16 Under these conditions the desired cyclononene product was obtained as an inseparable mixture of E- and Z-isomers (7 93). Interestingly, two sets of peaks observed in the1H NMR spectrum indicated that the Z-isomer existed as two separate conformers at room temperature. This intermediate was subsequently used in Murphy s approach to the radical-based preparation of tricyclic indoles. 

The cyclic vinyl ether (182),170 postulated last year as an intermediate in the 21-acetoxylation of the hemiacetal (183), can be prepared in good yield by heating the hemiacetal with aluminium isopropoxide in toluene under argon, followed by direct chromatography on basic alumina.171 The vinyl ether was converted into the 20,21-diol (184) either by reaction with osmium tetroxide or by acetoxylation with lead tetra-acetate, followed by hydrolysis. The hypoiodite reaction, followed by oxidation, allows direct conversion of a 21-acetoxypregnan-20/3-ol (185) into the 18-iodo-20-ketone (186), which is solvolysed in the presence of silver acetate to provide a new route to the 21-acetate of 18-hydroxydeoxycorticosterone hemiacetal (187).171... 

In order to obtain high enantioselectivities it seems to be important that the reactions proceed via cationic intermediates (e.g. 24) to disfavor the partial dissociation of the chiral ligand. For this reason, silver salts are added to reactions of vinyl-iodides. These reactions are best performed in Al-methylpyrrolidone (NMP) as a solvent. As the examples shown in Scheme 9 demonstrate, both c/s-decalin [12] and cA-hydrindane [13] derivatives can be obtained in useful yields and enantiomeric purities. 

Reaction of l-chloro-l,3,3-triphenylallene (19) with p-toluidine in the presence of silver triflate gave 2,3,4-triphenylbuta- l-aza-1,3-diene derivative 22a via a novel l, 2-phenyl shift not reported earlier in the solvolysis of allenyl chlorides. The reaction takes place via the formation of the allenyl cation, which is captured as its canonical propargyl cation, first affording the protonated amine 20 (R = Me). Proton transfer from the nitrogen to the acetylenic carbon is followed by migration of a phenyl group in the intermediate vinyl cation 21 (R = Me) to afford the iminium triflate 22a. The latter is hydrolyzed by aqueous sodium hydroxide to the azabutadiene 23 (equation 5). Similar reaction of 19 with aniline and silver triflate afforded the corresponding iminium triflate 22b. ... 

Free-radical reactions. Silver nitrate, sodium persulfate, and iron(III) nitrate constitute an oxidizing system that degrades carboxylic acids to radicals. Adding these reactive intermediates to radical acceptors such as methyl vinyl ketone, acrylic esters, and acrylonitrile initiates synthetically useful processes. Monoamides of oxalic acid undergo oxidative degradation by (NH )2SjOg in the presence of AgNOj-Cu(OAc)2 to afford isocyanates in a biphasic system (11 examples, 45-87%). ... 

The selective formation of the arylated or vinylated allylalcohol was rationalized by assuming a cationic four-manbered intermediate, in which the hydrogen atom (H ) on the hydroxyl-bearing carbon is located unfavorably for a syn palladium hydride elimination. The cationic intermediates were generated from organic triflates, iodonium salts,or organic iodide/thallium or silver salt combinations (Scheme 28). 

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