Gold-Catalyzed Reactions via Cyclopropyl Gold Carbene-like Intermediates

Gold-Catalyzed Regiodivergent [2 + 2 + 2]-Cycloadditions of Allenes with Triazines

Gold-catalyzed regiodivergent cycloadditions of functionalized allenes with 1,3,5-triazines, providing diverse N-heterocycles in moderate to excellent yields under mild reaction conditions, are reported. Importantly, different types of allenes exhibit distinct selectivity and reactivity for the reactions. Mechanistic investigations reveal that all of the cycloadditions proceed through a stepwise [2 + 2 + 2]-cycloaddition process.

Alkynyl sulfoxides as α-sulfinyl carbene equivalents: gold-catalysed oxidative cyclopropanation

Gold catalysed oxidation of alkynyl sulfoxides provides access to a desirable α-sulfinyl metal carbene reactivity profile that is inaccessible using diazo chemistry.

Gold(i)-catalyzed addition of aldehydes to cyclopropylidene bearing 6-aryl-1,5-enynes

A diastereoselective, gold-catalyzed cascading cycloisomerization of alkylidene cyclopropane bearing 1,5-enynes that terminates in a cyclo-addition of aldehydes has been developed. This diastereoselective reaction provides convergent access to novel polycyclic molecular structures (18 examples), and tolerates a diverse scope of aldehydes. Mechanistic studies reveal that the catalytic cycle rests at a digold off-cycle intermediate, one of which was isolated.

Platinum-catalysed intermolecular addition of carbonyl compounds to 1,6-enynes: investigation of a new reaction pathway

A novel intermolecular addition of aldehydes to 1,6-enynes via a Pt-carbene intermediate provides the diastereoselective formation of valuable tricyclic compounds.

α,β-Unsaturated Gold(I) Carbenes by Tandem Cyclization and 1,5-Alkoxy Migration of 1,6-Enynes: Mechanisms and Applications

1,6-Enynes bearing OR groups at the propargyl position generate α,β-unsaturated gold(I)-carbenes/ gold(I) stabilized allyl cations that can be trapped by alkenes to form cyclopropanes or 1,3-diketones to give products of α-alkylation. The best migrating group is p-nitrophenyl ether, which leads to the corresponding products without racemization. Thus, an improved formal synthesis of (+)-schisanwilsonene A has been accomplished. The different competitive reaction pathways have been delineated computationally.

Synthesis of Barbaralones and Bullvalenes Made Easy by Gold Catalysis

The gold(I)-catalyzed oxidative cyclization of 7-ethynyl-1,3,5-cycloheptatrienes gives 1-substituted barbaralones in a general manner, which simplifies the access to other fluxional molecules. As an example, we report the shortest syntheses of bullvalene, phenylbullvalene, and disubstituted bullvalenes, and a readily accessible route to complex cage-type structures by further gold(I)-catalyzed reactions.

Hydroacenes Made Easy by Gold(I) Catalysis

A novel strategy for the synthesis of partially saturated acene derivatives has been developed based on a Au^I‐catalyzed cyclization of 1,7‐enynes. This method provides straightforward access to stable polycyclic products featuring the backbone of the acene series, up to nonacene.

Divergent reaction pathways in gold-catalyzed cycloisomerization of 1,5-enynes containing a cyclopropane ring: dramatic ortho substituent and temperature effects

A gold(i)-catalyzed cycloisomerization of easily available 1,5-enynes containing a cyclopropane ring has been developed, efficiently providing cyclobutane-fused 1,4-cyclohexadiene, tricyclic cyclobutene, biscyclopropane and 1,3-cyclohexadiene derivatives in moderate to excellent yields. When the phenyl group was not ortho substituted, 1,4-cyclohexadienes could be produced. With an ortho substituent, three different products could be selectively synthesized by control of the temperature and the used gold(i) catalyst. The 1,5-enyne substrate first undergoes a classical enyne cycloisomerization to form a tricyclic cyclobutene key intermediate, which undergoes subsequent transformation to produce the desired products. A plausible reaction mechanism was proposed according to deuterium labeling experiments and intermediate trapping experiments, as well as DFT calculations. In our current reaction, the ortho substituent on the phenyl group controls the reaction outcome and the ortho substituent effect was found to originate from steric and electronic factors.

Broad Scope Aminocyclization of Enynes with Cationic JohnPhos-Gold(I) Complex as the Catalyst

A practical aminocyclization of 1,6-enynes with a wide variety of substituted anilines, including N-alkyl anilines, has been achived by using cationic [JohnPhosAu(MeCN)]SbF₆ as a general purpose catalyst. The resulting adducts can be easily converted into polycyclic compounds by palladium- and gold-catalyzed reactions.

Gold(I)-Catalyzed Inter- and Intramolecular Additions of Carbonyl Compounds to Allenenes

The gold(I)-catalyzed intramolecular reaction of allenes with oxoalkenes leads to bicyclo[6.3.0]undecane ring systems, although in the case of terminally disubstituted allenes, seven-membered rings are formed. The related intermolecular addition of aldehydes to allenenes also gives seven-membered rings.

Exploring the gold mine: [Au]-catalysed transformations of enynals, enynones and enynols

This review highlights reactions of enynals, enynones and enynols using gold catalysis which often lead to cycloaddition or cyclisation products.

Beyond Fischer and Schrock carbenes: non-heteroatom-stabilized group 6 metal carbene complexes – a general overview

Non-heteroatom-stabilized group 6 metal carbene complexes: versatile reagents or intermediates in stoichiometric or catalytic reactions in organic synthesis.

Ligand-controlled gold-catalyzed cycloisomerization of 1,n-enyne esters toward synthesis of dihydronaphthalene

We describe herein a gold-catalyzed rearrangement of propargyl esters followed by allene–ene cyclization to afford substituted bicyclic [4.4.0] dihydronaphthalene compounds.

Divergent C-H Insertion-Cyclization Cascades of N-Allyl Ynamides

Gold carbene reactivity patterns were accessed by ynamide insertion into a C(sp(3) )H bond. A substantial increase in molecular complexity occurred through the cascade polycyclization of N-allyl ynamides to form fused nitrogen-heterocycle scaffolds. Exquisite selectivity was observed despite several competing pathways in an efficient gold-catalyzed synthesis of densely functionalized C(sp(3) )-rich polycycles and a copper-catalyzed synthesis of fused pyridine derivatives. The respective gold-keteniminium and ketenimine activation pathways have been explored through a structure-reactivity study, and isotopic labeling identified turnover-limiting CH bond-cleavage in both processes.

Cyclopropanation/Carboboration Reactions of Enynes with B(C6F5)3

Stoichiometric reaction of B(C6F5)3 with 1,6-enynes is shown to proceed via initial cyclopropanation and formal 1,1-carboboration. Depending on the substitution on the alkene moiety, subsequent ring-opening of the cyclopropane affords either cyclopentane or cyclohexane derivatives in which the C6F5 and B(C6F5)2 adopt a 1,4-positioning. Mechanistically, this transformation involves π-activation of the alkyne moiety, which triggers cyclopropanation, followed by carboboration. Both the cyclopropanation and subsequent ring-opening are shown to be stereospecific. Both cyclopropanation and 1,4-carboborated products were employed as Lewis acid components in frustrated Lewis pair activation of H2 and CO2.