Gold-catalyzed substitution reaction with ortho-alkynylbenzoic acid alkyl ester as an efficient alkylating agent

Esterification and Etherification of Aliphatic Alcohols Enabled by Catalytic Strain-Release of Donor-Acceptor Cyclopropane

We herein disclose a highly efficient protocol for the esterification and etherification of alcohols, leveraging a Sc(OTf)3-catalyzed ring-strain release event in the meticulously designed, chromatographically stable mixed anhydrides or benzyl esters that incorporate an intramolecular donor-acceptor cyclopropane (DAC). This versatile method facilitates the straightforward functionalization of sugar, terpene, and steroid alcohols under mild acidic conditions, as showcased by the single-catalyst-driven, dual protection of sugar diol.

Dienylation of Unfunctionalized Arenes with 1,6-Diynes via Rhodium-Catalyzed Directing-Group-Free C–H Bond Activation

It has been established that the dienylation of unfunctionalized arenes with 1,6-diynes, possessing aryl groups at the diyne termini, proceeds to give the corresponding dienylated arenes in the presence of a catalytic amount of an electron-deficient cyclopentadienyl rhodium(III) complex, [CpERhCl2]2, and a stoichiometric amount of silver carbonate. Experimental and theoretical mechanistic studies revealed that a CpERh(I) complex generated in situ might catalyze the present dienylation­ reaction.

Cycloisomerization of π-Coupled Heteroatom Nucleophiles by Gold Catalysis: En Route to Regiochemically Defined Heterocycles

Since the dawn of millennium, catalytic gold chemistry is at the forefront to set off diverse organic reactions via unique activation of π-bonded molecules. Within this purview, cycloisomerization of heteroatom nucleophiles linked to a π-system is one of the well recognized chemistry for the construction of numerous heterocyclic cores. Though the rudimentary aspects of this transformation are reviewed by several groups in different timeline, a holistic view on regiochemistry of such reactions went largely overlooked. Hence, this account emphasizes the gold catalyzed regioselective cycloisomerization of structurally distinctive π-connected hetero-nucleophiles leading to different heterocycles documented in the last two decades. From an application perspective, this account also highlights those methodologies which find a role in the total synthesis of natural products. Wherever appropriate, mechanistic details and contributing factors for selectivity are also discussed.

Boron insertion into alkyl ether bonds via zinc/nickel tandem catalysis

Mild methods to cleave the carbon-oxygen (C-O) bond in alkyl ethers could simplify chemical syntheses through the elaboration of these robust, readily available precursors. Here we report that dibromoboranes react with alkyl ethers in the presence of a nickel catalyst and zinc reductant to insert boron into the C-O bond. Subsequent reactivity can effect oxygen-to-nitrogen substitution or one-carbon homologation of cyclic ethers and more broadly streamline preparation of bioactive compounds. Mechanistic studies reveal a cleavage-then-rebound pathway via zinc/nickel tandem catalysis.

Nonclassical Mechanism in the Cyclodehydration of Diols Catalyzed by a Bifunctional Iridium Complex

1,4- and 1,5-diols undergo cyclodehydration upon treatment with cationic N-heterocyclic carbene (NHC)-IrIII complexes to give tetrahydrofurans and tetrahydropyrans, respectively. The mechanism was investigated, and a metal-hydride-driven pathway was proposed for all substrates, except for very electron-rich ones. This contrasts with the well-established classical pathways that involve nucleophilic substitution.

Gold-catalyzed glycosylation in the synthesis of complex carbohydrate-containing natural products

Gold(i)- and gold(iii)-catalyzed glycosylation reactions and their application in the synthesis of natural glycoconjugates are reviewed.

Gold-silver catalyzed straightforward one pot synthesis of pyrano[3,4-b]pyrrol-7(1H)-ones

Pyrano[3,4-b]pyrrol-7(1H)-one is a bicyclic structure that is rarely described in the literature but is found in numerous polycyclic natural products as lamellarins. This work presents a one-pot synthesis of pyrano[3,4-b]pyrrol-7(1H)-one substituted in the 2- and 5-position. The reaction proceeds via a one-pot two step 5-endo-dig and 6-endo-dig cyclization catalyzed by a cationic gold complex with high regioselectivity.

Cyclic ether synthesis from diols using trimethyl phosphate

Cyclic ethers are simply synthesized from diols by using trimethyl phosphate at room temperature.

Gold(i)-catalyzed C-glycosylation of glycosyl ortho-alkynylbenzoates: the role of the moisture sequestered by molecular sieves

C-Glycosylation of glycosyl ortho-hexynylbenzoates with allyltrimethylsilane or silyl enol ethers could proceed smoothly under the catalysis of Ph₃PAuNTf₂, wherein the moisture sequestered by the molecular sieves ensured the gold(i)-catalytic cycle.

An efficient synthesis of highly substituted indanones and chalcones promoted by superacid

A superacid promoted one-pot method was developed for the efficient synthesis of indanones. This process enabled the formation of a dual C–C bond between the aryl isopropyl ketones and benzaldehydes. Interestingly, when the reaction was performed between acetophenones and benzaldehydes, it was impeded after the aldol condensation and resulted in the corresponding chalcones.

Breaking the dichotomy of reactivity vs. chemoselectivity in catalytic SN1 reactions of alcohols

B(C₆F₅)₃ possesses a different reactivity/chemoselectivity profile than traditional Lewis and Brønsted acids and is effective at enabling catalytic S_N1 reactions of alcohols in the presence of acid sensitive groups without compromising reaction rates, substrate scope or catalyst loadings.

[3,3]-Sigmatropic rearrangement step in the gold-catalyzed cyclization of allyl-(ortho-alkinylphenyl)methyl ethers

The gold-catalyzed conversion of allyl-(ortho-alkynylphenyl)methyl ethers was investigated, and allylated isochromenes were obtained. An optimization of the catalysis conditions with respect to different phosphane and carbene ligands on gold, different counterions, and different solvents was conducted. Subsequently, the scope and limitations of this reaction were investigated with 21 substrates. The mechanistic studies show an allylic inversion, as supported by NMR data and an X-ray crystal structure analysis, as well as an intermolecular reaction, as determined by crossover experiments. There is no competition of protodeauration even in the presence of water. All these observations differ from other related conversions and clearly indicate product formation by a [3,3]sigmatropic rearrangement in the step forming the new C-C bond.

Complexity-generating hydration reactions via gold-catalyzed addition of boronic acids to alkynes

Boronic acids can serve as organic soluble substitutes for water molecules in the metal-catalyzed hydration of alkynes. The Au-catalyzed addition of boronic acids to alkynes provides an alternative method for enolate generation, which proceeds under exceptionally mild conditions. The resulting enolates can be trapped by aldehydes present in the reaction mixture, giving aldol products that can be isolated as cyclic borate esters. These compounds are versatile synthetic intermediates that can be elaborated into a variety of products by transformation of the boron moiety. The Au-catalyzed reaction of boronic acids with propargylic alcohols results in efficient Meyer–Schuster rearrangement to the corresponding enones. The rearrangement of tertiary alcohols gives (E)-enones with moderate to good selectivity, and the addition of a boronic acid to the reaction appears to enhance the level of geometrical control. The rearrangement of primary alcohols to terminal enones also occurs readily in the presence of catalytic Au(I) and a boronic acid, and the resulting terminal enones can be reacted with nucleophiles in one-pot procedures to give a variety of β-substituted ketones.

Gold-catalyzed alkylation of silyl enol ethers with ortho-alkynylbenzoic acid esters

Unprecedented alkylation of silyl enol ethers has been developed by the use of ortho-alkynylbenzoic acid alkyl esters as alkylating agents in the presence of a gold catalyst. The reaction probably proceeds through the gold-induced in situ construction of leaving groups and subsequent nucleophilic attack on the silyl enol ethers. The generated leaving compound abstracts a proton to regenerate the silyl enol ether structure.

Catalyzed catalysis using carbophilic Lewis acidic gold and Lewis basic palladium: synthesis of substituted butenolides and isocoumarins

A new strategy for gold and palladium dual-catalytic reactivity and turnover, called catalyzed catalysis, enhanced the synthetic usefulness of vinylgold intermediates by providing dual-catalytic carbon-carbon cross-coupling as an alternative to protodemetalation. This protocol enabled the synthesis of substituted butenolides and isocoumarins from allyl esters. Kinetic and spectroscopic experiments support a mechanism in which the Lewis acidic gold complex catalyzes both an initial rearrangement step and a subsequent Lewis basic palladium oxidative-addition step.