Gold-catalyzed intermolecular hydroalkoxylation of allenes; difference in mechanism between hydroalkoxylation and hydroamination

A wide range of alcohols 2 react with various allenes 1 in the presence of ClAuPPh₃/AgOTf catalyst at ambient temperature without solvent to produce allylic ethers 3. Contrary to the hydroamination, which proceeds through high chiral-face selectivity for chiral allenes to give the corresponding chiral allylic amines, transfer of chirality is not observed in the hydroalkoxylation, suggesting that the mechanism of the gold-catalyzed hydroalkoxylation is different from that of hydroamination.     

Gold-catalyzed highly enantioselective synthesis of axially chiral allenes

Axially chiral allenes are synthesized from chiral propargylamines catalyzed by KAuCl4 in high yields (up to 93% yield) and excellent enantioselectivities (up to 97% ee) in CH3CN at 40 degrees C. The reaction has been applied to the synthesis of novel allene-modified artemisinin derivatives with the delicate endoperoxide moieties remaining intact. A tentative mechanism regarding gold(I)-catalyzed intramolecular hydride transfer was proposed on the basis of deuterium-labeling experiments and ESI-MS analysis of the reaction mixture.     

Gold-catalyzed intramolecular hydroamination of allenes: a case of chirality transfer

The hydroamination of allenes proceeded smoothly in the presence of gold catalysts to give the corresponding 2-vinyl pyrrolidines and piperidines in high yields. The reaction is very efficient and can be carried out with only 1-5 mol % catalyst at room temperature and under extremely mild conditions. As an example of chirality transfer, it is shown that aminoallene 1a (96% ee), synthesized from (S)-(−)-1-octyn-3-ol, was converted into the corresponding pyrrolidine 2a (94% ee) in 99% yield.     

Gold-catalyzed isomerization of unactivated allenes into 1,3-dienes under ambient conditions

We have developed a gold-catalyzed isomerization of unactivated allenes into 1,3-dienes with nitrosobenzene as an additive. This reaction proceeded almost exclusively at room temperature for highly substituted allenes. The utility of this reaction is manifested by the development of one-pot [4+2]-cycloaddition of allenes and reactive alkenes.     

Golden times for allenes: Gold-catalyzed cycloisomerization of beta-hydroxyallenes to dihydropyrans

The gold(I)-catalyzed 6-endo cycloisomerization of beta-hydroxyallenes provides a mild and efficient access to chiral functionalized dihydropyrans which were obtained at room temperature in good chemical yields with axis-to-center chirality transfer. The method was extended to the beta-aminoallene 12, which afforded tetrahydropyridine 13 in good yield as well.     

Gold-catalyzed hydrofunctionalization of allenes with nitrogen and oxygen nucleophiles and its mechanistic insight

A wide range of nucleophiles, such as amines and alcohols, reacted intermolecularly with various allenes in the presence of gold catalysts to give the corresponding hydrofunctionalization products in high yields. The intermolecular hydroamination of chiral allenes with aromatic and aliphatic amines proceeded with high to good enantioface selectivities to afford the corresponding chiral allylic amines. On the other hand, in the case of the intermolecular hydroalkoxylation of chiral allenes, no chirality transfer was observed. This marked contrast on the chirality transfer indicates that the mechanisms of gold-catalysis between hydroamination and hydroalkoxylation are different.     

Gold-catalyzed intermolecular [4C+3C] cycloaddition reactions

In the presence of the N-heterocyclic carbene gold catalyst (NHC-AuIPr, 7), propargyl esters 1a-f and 13 undergo a [4C+3C] cycloaddition reaction with cyclopentadiene and furan under mild conditions. The evidence suggests that the formation of the seven-membered ring occurs by a direct cycloaddition process, rather than a stepwise cyclopropanation/Cope rearrangement sequence.     

Gold-catalyzed hydroarylation of allenes: a highly regioselective carbon-carbon bond formation producing six-membered rings

Gold-catalyzed intramolecular hydroarylation of allenic anilines and phenols offers an efficient route to dihydroquinoline and chromene derivatives under mild reaction conditions. The hydroarylation takes place at the terminal or central allenic carbon depending on the substrate structure, leading to a highly selective formation of six-membered rings.     

Transition metal-catalysed intermolecular reaction of allenes with oxygen nucleophiles: a perspective

Transition metal catalysed hydroalkoxylation of allenes has received much attention in recent years, and both the intra- and intermolecular versions have been reported. Gold(I) complexes are among the most active catalysts for these processes. This critical perspective article will cover the progress in this field, analysing the intermolecular metal-catalysed reaction of allenes using palladium, iridium, rhodium, ruthenium, gold and platinum, in the presence of alcohols, water or carboxylic acids, and the mechanistic implications of these processes depending on the metal used.     

Gold-catalyzed intermolecular addition of alcohols toward the allenic bond of 4-vinylidene-2-oxazolidinones

Gold catalyzed intermolecular addition of alcohols toward the proximal allenic double bond of 4-vinylidene-2-oxazolidinones gives hydroalkoxylation products, which can be easily converted into the corresponding novel spiro dihydrofuran or dihydropyran derivatives in high yield.     

Synthesis of allenes via gold-catalyzed intermolecular reaction of propargylic alcohols and aromatic compounds

Functionalized allenes are efficiently synthesized in moderate to high yield from gold-catalyzed intermolecular reaction of propargylic alcohols and aromatic compounds. The user-friendly process could be conducted under mild reaction conditions with easily accessible starting materials.     

Gold-catalyzed formation of oxonium ions from enynes and their intra- and intermolecular trapping with allylsilanes

Gold-catalyzed ring closure of 1,5-enyne containing a silyl ether at the allylic position induces a skeletal rearrangement to form an oxonium intermediate, which then undergoes a smooth allylation in both an intra- and intermolecular manner. In the intramolecular allyl transfer, the additive alcohol becomes positioned on the silicon of the silyl ether by forming a new Si-OR bond, whereas, in the intermolecular allylation, the alcohol is incorporated in the homoallylic carbon by forming a C-OR bond.     

Mild rhodium(III)-catalyzed C-H activation and intermolecular annulation with allenes

All(enes) great! A novel Rh(III)-catalyzed oxidative coupling with allenes under mild conditions provides heterocycles with exocyclic double bonds. This reaction features low catalyst loadings, high regio- and stereoselectivity, and excellent substrate scope. The products were derivatized and preliminary mechanistic studies were conducted.     

Gold(I)-catalyzed intermolecular hydroarylation of allenes with nucleophilic arenes: scope and limitations

The addition of nucleophilic methoxyarenes to allenes proceeds at room temperature in dichloromethane with a catalytic amount of phosphite-gold(I) precatalyst and silver additive. The addition is regioselective for the allene terminus, and generates E-allylation products without the need for prefunctionalization of the synthons as organometallics or allyl bromides. Coordinating heteroaromatics and sterically hindered allenes do not participate in the reaction.     

Gold-catalyzed intermolecular hetero-dehydro-diels-alder cycloaddition of captodative dienynes with nitriles: a new reaction and regioselective direct access to pyridines

For the first time, nitriles are used as 2pi electron component in a gold-catalyzed intermolecular hetero-dehydro-Diels-Alder cycloaddition with captodative enynes leading to the regioselective formation of pyridines.