Propargyl silver -catalyzed

Li and coworkers have reported a novel silver-catalyzed, three-component coupling of an aldehyde, an amine, and an alkyne, and the first example of a direct addition of a silver acetylide to an aldehyde to produce propargylic alcohols (Scheme 1.41).103-105 Treatment of an aldehyde with a silver halide and secondary amine gave propargylic amines in good yields in organic solvent, water, or ionic liquids. The proposed mechanism suggests addition of a silver acetylide to the iminium ion formed in situ. 

Further mechanistic work with optically active and labeled compounds confirmed that the rate-determining step in such rearrangement was the silver coordination to the alkyne moiety and revealed that the silver-catalyzed allene epimerization was 2-40 times faster than the propargyl ester rearrangement.53... 

It is worth noting that a silyl group at the propargyl position did not interfere with the silver-catalyzed rearrangement of a propargyl acetate, despite the potential for further evolution of the product (Scheme 3.34).55... 

The silver-catalyzed, propargyl Claisen rearrangement has also been combined with cyclization reactions. Propargyl ethers derived from [3-ketoesters were rearranged by silver hexafluoroantimonate and the resulting allenic [3-ketoesters cyclized on treatment with base, leading to the formation of 2/7-pyrans in moderate to excellent yields (Scheme 3.48).75 The cyclization process was described as a base-catalyzed... 

Very recently, Davies and coworkers have reported a silver-catalyzed Doyle-Kirmse reaction of ally lie and propargylic sulfides with ethyl diazophenylacetate (35). A selection of examples was investigated providing the rearranged products, either homoallylic thioethers (76 —> 77, Scheme 8.14a) or allenyl thioethers (78 —> 79, Scheme 8.14b) in good yields, and with good overall scope.40... 

The silver-catalyzed cycloisomerization of allenic carboxylic acids to butenolides was also reported by Marshall and co-workers.329 Starting from the enantiomerically enriched propargyl mesylate 390, palladium-catalyzed hydroxycarbonylation led to the chiral allenecarboxylates 391 which afforded the butenolides 392 upon treatment with silver nitrate (Scheme 114). Unfortunately, partial racemization could not be avoided in this two-step sequence. In a related study, Ma and Shi330 have shown that the combination of Pd(PPh3)4 and Ag2C03 promotes the cyclization of allenecarboxylates to the corresponding butenolides, accompanied by the introduction of aryl or alkenyl groups at C3. 

Figure 28. Silver-catalyzed carbene insertion into allyUc and propargylic C—X bonds.

A range of thiazoles with various combinations of Ri, R2, and R3 substituents was synthesized using this method. The silver-catalyzed cycloaddition of propargylic alcohol with thioamide was proposed to proceed through the intermediacy of a propargylic cation or the corresponding allenyl cation and its subsequent reaction with the nucleophilic sulfiir of thioamide, followed by a 5-exo-dig attack by nitrogen. 

Dalla, V. and Pale, P. 1999. Silver-catalyzed cyclization of acetylenic alcohols and acids A remarkable accelerating effect of a propargylic C-O bond. New J. Ghent. 23 ... 

Kirsch has reported the conversion of propargyl vinyl ethers to form pyrroles via a multi-step transformation involving the silver-catalyzed propargyl Claisen rearrangement to form the a-allenyl P-keto ester, condensation with a primary aryl amine. 

Intramolecular nitrogen attack in propargylated enaminones allows silver-catalyzed access to functionalized pyrroles. This Ag-promoted hydroamination can also be used to obtain A bridgehead pyrroles. Silver nitrate-mediated cyclization of allenylamines, available from Uthiated alkoxy allenes and imines or through reaction of l-(lV-carbamoyl)-alkylcuprates with propargyl substrates, provides access to 2,5-dihydropyrrole derivatives. Iminoallenes can be used for the synthesis of substituted p)moles in moderate yields in the presence of potassium carbonate. ... 

W. Yamada, Y. Sugawara, H.M. Cheng, T. Ikeno, T. Yamada, Silver-catalyzed incorporation of carbon dioxide into propargylic alcohols, Eur. J. Qrg. Chem. (2007) 2604-2607. 

H.-F. Jiang, J.-W. Zhao, Silver-catalyzed activation of internal propargylic alcohols in supercritical carbon dioxide efficient and eco-friendly synthesis of 4-alkylidene-l,3-oxazoHdin-2-ones, Tetrahedron Lett. 50 (2009) 60-62. 

Rearrangements of propargyl esters with silver salts were first mentioned by Zakharova in the mid-1940s.49 He described the conversion of 3-chloro-3-methyl-but-l-yne into a mixture of acetates in which the allenic acetate, l-acetoxy-3-methylbut-1,2-diene, was the major compound (Scheme 3.30). Although this product could arise from a silver assisted SN2 reaction, it could also be produced from the substitution product through rearrangement, probably catalyzed by silver ions. 

In another related and well-known [3,3]-sigmatropic shift usually performed under thermal conditions, the propargyl-Claisen rearrangement,62 silver salts were also able to catalyze the reaction. Silver tetrafluoroborate and hexafluoroantimonate proved to be the best catalysts for this reaction, leading quantitatively to allenic p-ketoesters when starting from propargyl ethers derived from p-ketoesters (Scheme 3.41).63 64... 

In related reactions, Snapper and Hoveyda et al. reported an asymmetric version of Mannich-type reactions catalyzed by silver acetate.38,39 Propargyl imines proved to be susceptible to nucleophilic addition of sily lenol ethers derived from acetate esters in the... 

The rather unusual precatalyst silver(i) isocyanate was found to efficiently catalyze the cyclization of propargyl carbamates 420 to 4-alkylideneoxazolidin-2-ones 421 in good to high yields (Scheme 123).348 The presence of a base such as potassium /-butoxide or triethylamine is required for formation of the amide nucleophile which undergoes a stereoselective intramolecular attack at the activated triple bond (/rstereo-isomer 421 exclusively. Likewise, homopropargyl carbamates are converted into six-membered (Z)-4-alkylidene-l,3-oxazinane-2-ones under the same conditions. 

Li and co-workers374,374a reported the three-component coupling reaction of an aldehyde, an amine, and a terminal alkyne catalyzed by a silver salt in water. Of various precatalysts examined, water-insoluble silver iodide gave the highest yields of the propargyl amines 452 (Scheme 137). The reaction probably proceeds via attack of a silver acetylide, generated in situ from the silver salt and the alkyne, to the iminium ion derived from the aldehyde and the... 

Oxazolidines are obtained in good to excellent yields by the palladium(II)-catalyzed cyclization of A-Boc protected iV-allyl-A -hydroxymethylamines (191) <94CC357>. The palladium species is regenerated by molecular oxygen in DMSO (Scheme 94). Allyl carbamoylmethyl ethers cyclize to oxazolidines by reaction with mercuric acetate <89H(28)663>. Silver triflate catalyzes the cyclization of (9-propargyl isoureas to 4-alkylidene-oxazolidines with high diastereoselectivity <88CC1175>. 

On the other hand, propargyl vinyl ethers 82 with no additional substituent at the vinylic position were smoothly converted into 1,2-dihydropyridines 85 (Scheme 28). While the initial rearrangement was catalyzed best by the action of gold(I) chloride instead of silver(I) hexafluoroantimonate, the sequential addition of an amine and 20mol% of p-toluenesulfonic acid... 

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