Intermolecular Homopropargyl Alcohol Addition to Alkyne and a Sequential 1,6-Enyne Cycloisomerization with Triazole-Gold Catalyst

Electrochemical C(sp2)-H/N-H "formal" cross-dehydrogenative coupling of olefins with benzotriazoles for synthesis of N-vinyl benzotriazoles

The paper details an electrochemical method that couples olefins with benzotriazoles to form C(sp2)-N bonds, enabling the synthesis of N-vinyl benzotriazoles in moderate to good yields. nBu4NI functions as both an electrolyte and an iodine mediator, and the method does not require oxidants or metals. It is a highly atom-economical and clean reaction, with hydrogen as the sole byproduct.

Base-Promoted Decarboxylative Annulation of Methyl 2-(2-Bromophenyl)acetates and Ynones to Access Benzoxepines

A simple and efficient base-mediated decarboxylative annulation of ynones with methyl 2-(2-bromophenyl)acetates has been developed. A broad range of benzoxepines were prepared with a broad substrate scope and high regioselectivity in moderate to excellent yields under transition-metal-free conditions. This method proceeds through a tandem [2 + 4] annulation, ring-opening decarboxylative reaction, and the intramolecular nucleophilic aromatic substitution reaction. Additionally, the key intermediates were successfully obtained and characterized unambiguously by single-crystal X-ray crystallography, which could favorably support a decarboxylative annulation mechanism. Furthermore, gram-scale reaction and synthetic applications for the further functionalization are also studied.

Catalyst-controlled cycloisomerization/[4+3] cycloaddition sequence to construct 2,3-furan-fused dihydroazepines and 2,3-pyrrole-fused dihydrooxepines

A novel catalyst-controlled cycloisomerization/[4+3]cycloaddition sequence of readily available acyclic enyne-amides and crotonate-derived sulfur ylides is reported. This strategy enables the rapid and efficient construction of a series of bicyclic 2,3-furan-fused...

Facile synthesis of diverse hetero polyaromatic hydrocarbons (PAHs) via the styryl Diels–Alder reaction of conjugated diynes

The intramolecular styryl Diels–Alder reaction with conjugated diynes under thermally stable triazole-gold (TA–Au) catalytic conditions and the sequential transformation through alkyne activation to access various PAHs with high efficiency was reported for the first time.

Lewis-Acid-Catalyzed Tandem Cyclization by Ring Expansion of Tertiary Cycloalkanols with Propargyl Alcohols

A new method for the efficient synthesis of hexahydro-1H-fluorene and octahydrobenzo[a]azulene derivatives through a ring-expansion strategy is reported. With an appropriate combination of thulium(III) trifluoromethanesulfonate and 13X molecular sieves, a range of unsaturated polycyclic compounds were obtained in good yields. Mechanism studies reveal that the reaction is more likely to undergo Meyer-Schuster rearrangement, ring expansion, and Friedel-Crafts-type pathways, which provide a conceptually different strategy for the ring opening of tertiary cycloalkanols.

Diastereoselective [2+2+1] Hydrative Annulation of Phenol-Linked 1,6-Enynes with Acetylenes Through Rhodium Catalysis: A Rapid Access to Cyclopenta[b]benzofuranols

An unprecedented [2+2+1] hydrative annulation of 1,6-enynes with terminal alkynes is achieved using catalytic cationic Rh(I). Thus, a modular assembly of cyclopenta[b]benzofuranols with two consecutive quarternary stereocenters is achieved from readily available alkynes. The reaction is proposed to go through a sequence of 5-membered rhoda-cycle formation, regioselective acetylene insertion, 1,5 H-shift, substrate controlled stereoselective addition of water molecule followed by 1,2-rhodium migration gave contracted rhoda-cycle D and reductive elimination. Necessary control/labelling experiments were conducted to gain insight in to the mechanism.

Achieving Aliphatic Amine Addition to Arylalkynes via the Lewis Acid Assisted Triazole-Gold (TA-Au) Catalyst System

Transition metal catalyzed intermolecular hydroamination of the arylalkynes with aliphatic amine is generally problematic due to the good coordination between amine and metal cation. With the combination of 1,2,3-triazole coordinated gold(I) catalyst (TA-Au) and Zn(OTf)₂ cocatalyst, this challenging transformation was achieved with good to excellent yields and regioselectivity. Compared to previously reported methods, this approach offered an alternative catalyst system to achieve this fundamental chemical transformation with high efficiency and practical conditions.

Diazo Activation with Diazonium Salts: Synthesis of Indazole and 1,2,4-Triazole

A donor/acceptor diazo activation strategy, processing via condensation using diazonium salts without the addition of any other catalysts or reagents, is reported. The diazenium intermediate was found to undergo cyclization to give indazoles in excellent yields. Alternatively, in the presence of nitriles, substituted 1,2,4-triazoles were obtained in good to excellent yields. This interesting diazenium route provides a new approach to achieve complex heterocycle synthesis under mild conditions.

Ethyl 5-[(ethoxycarbonyl)oxy]-5,5-diphenylpent-2-ynoate

The title compound, C22H22O5, crystallizes with two molecules in the asymmetric unit, one of which shows disorder of its ethyl acetate group over two sets of sites in a 0.880 (2):0.120 (2) ratio. The C[triple-bond]C distances in the two molecules are almost the same [1.1939 (16) and 1.199 (2) Å], but the Csp 3—C[triple-bond]C angles differ somewhat [175.92 (12) and 172.53 (16)°]. In the crystal, several weak C—H...O interactions are seen.

Gold-Catalyzed Hydroalkoxylation/Povarov Reaction Cascade of Alkynols with N-Aryl Imines: Synthesis of Tetrahydroquinolines

A one-pot gold-catalyzed hydroalkoxylation/Povarov reaction cascade of alkynols with N-aryl imines or in situ generated iminium has been developed. The protocol provides a facile access to a series of fused tricyclic tetrahydroquinolines with a broad substrate scope using readily available materials under mild conditions. The unique mechanistic feature is the dual function of the gold catalyst, which first catalyzed the intramolecular hydroalkoxylation of alkynols, and upon the formation of dihydrofuran species, promoted the following Povarov reaction with high stereoselectivity.

Copper-Catalyzed Cascade Cyclization of Indolyl Homopropargyl Amides: Stereospecific Construction of Bridged Aza-[n.2.1] Skeletons

Catalytic cycloisomerization-initiated cascade cyclizations of terminal alkynes have received tremendous interest, and been widely used in the facile synthesis of a diverse array of valuable complex heterocycles. However, these tandem reactions have been mostly limited to noble-metal catalysis, and are initiated by an exo-cyclization pathway. Reported herein is an unprecedented copper-catalyzed endo-cyclization-initiated tandem reaction of indolyl homopropargyl amides, where copper catalyzes both the hydroamination and Friedel-Crafts alkylation process. This method allows the practical and atom-economical synthesis of valuable bridged aza-[n.2.1] skeletons (n=3-6) with wide substrate scope, and excellent diastereoselectivity and enantioselectivity by a chirality-transfer strategy. Moreover, the mechanistic rationale for this novel cascade cyclization is also strongly supported by control experiments, and is distinctively different from the related gold catalysis.

Theoretical Insight into the Au(I)-Catalyzed Intermolecular Condensation of Homopropargyl Alcohols with Terminal Alkynes: Reactant Stoichiometric Ratio-Controlled Chemodivergence

The mechanisms and chemoselectivities on the Au(I)-catalyzed intermolecular condensation between homopropargyl alcohols and terminal alkynes were investigated by performing DFT calculations. The reaction was indicated to involve three stages: transformation of the homopropargyl alcohol (R₁) via intramolecular cyclization to the cyclic vinyl ether (R₁'), formation of the C-2-arylalkynyl cyclic ether (P₁) via hydroalkynylation of R₁' with phenylacetylene (R₂), and conversion from P₁ to 2,3-dihydro-oxepine (P₂). The results revealed the origin of the reaction divergence and rationalized the experimental observations that a 1:3 reactant stoichiometric ratio affords P₁ as the major product, whereas the 1:1.1 ratio results in P₂ in high yield. The reactant stoichiometric ratio-controlled divergent reactivity is attributed to different catalytic activities of the gold catalyst toward different reaction stages. In the 1:3 situation, the excess R₂ induces the Au catalyst toward its dimerization and/or hydration, inhibiting the conversion of P₁ to P₂ and resulting in product P₁. Without excess R₂, the Au catalysis follows a general cascade reaction, leading to product P₂. Theoretical results described a general strategy controlling the reaction divergence by a different reactant stoichiometric ratio. This strategy may be enlightening for chemists who are exploring various synthesis methods with high chemo-, regio-, and enantioselectivities.

Highly N2-selective allylation of NH-1,2,3-triazoles with allenamides mediated by N-iodosuccinimide

We report a new protocol to synthesize N²-allyl-substituted 1,2,3-triazoles via NIS mediated allylation of allenamides with NH-1,2,3-triazoles.

Synthesis, characterization of active Sn(0), and its application in selective propargylation of aldehyde at room temperature in water

Active Sn(0) particles are synthesized in high yields by the chemical reduction of the blue–black stannous oxide using freshly prepared sodium stannite solution as reducing agent at 40 °C and 60 °C. The Sn(0) particles are characterized using powder XRD, SEM, and DSC. The as-synthesized Sn(0) particles are applied as reagent for the regioselective synthesis of homopropargyl alcohols from propargyl bromide and aldehydes in distilled water at room temperature (in 50%–84% yields). No assistance of heat, microwave, ultrasound, organic co-solvent, co-reagent, or inert atmosphere is required for this reaction. The propargylation reaction is highly chemoselective towards aldehyde over other less electrophilic carbonyl functional groups such as ketone, amide, and carboxylic acid. Our in-house synthesized homopropargyl alcohols can be used to synthesize conjugated 1,3-diynes.

1,1-Diphenyl-4-(thiophen-2-yl)but-3-yn-1-ol

The asymmetric unit of the title homopropargyl alcohol, C20H16OS, contains two independent molecules comprising a hydroxy group, a 3-(2-thiophenyl)propargylic moiety and two aromatic rings linked to a central carbon atom. The two unique molecules are linked into a dimer by an O—H...O hydrogen bond. In one molecule, the thiophene ring is disordered over two orientations rotated by 180° with a refined occupancy ratio of 0.575 (4):0.425 (4). The crystal structure is stabilized by O—H...π and C—H...π hydrogen-bond interactions. The crystal studied was a two-component non-merohedral twin, the refined ratio of the twin components being 0.575 (4):0.425 (4).

Homopropargyl alcohol 1,1-diphenylbut-3-yn-1-ol

The asymmetric unit of the title compound, C16H14O, contains one molecule with a central carbon atom having a distorted tetrahedral geometry made of a propargylic fragment, a hydroxy group and two aromatic rings. Directional interactions such as unusual O—H...π contacts are observed between the molecules in the crystal.

Homopropargyl alcohol 5,5-diphenylpent-2-yne-1,5-diol

In the title compound, C17H16O2, the central carbon atom has a distorted tetrahedral geometry [spread of angles = 105.71 (8)–112.75 (9)°] for its bonds to a homopropargylic but-2-yn-1-ol moiety, a hydroxy group and two phenyl substituents. In the crystal, O—H...O hydrogen-bonding interactions link the molecules into [001] chains and C—H...π(ring) contacts consolidate the packing.

Gold(I)-catalyzed Benzylation of (Hetero)aryl Boronic Acids with (Hetero)benzyl Bromides by the Strategy of a SN 2-type Reaction

Herein, the first example of gold-catalyzed benzylation of (hetero)aryl boronic acids with (hetero)benzyl bromides to give the corresponding cross-coupling products in moderate to good yields is reported. The reaction proceeds through a possible intermolecular S_N 2-type reaction pathway to give a wide variety of di(hetero)arylmethanes as the desired products. An intriguing reaction mechanism has been proposed on the basis of control experiments, ³¹ P-NMR spectroscopic detection and DFT calculations.

Gold(i) catalyzed cascade cyclization: intramolecular two-fold nucleophilic addition to vinylidenecyclopropanes (VDCPs)

A gold catalyzed cascade cyclization of vinylidenecyclopropanes to give spiro[cyclopenta[a]naphthalene-1,1′-cyclopropanes] in moderate to good yields upon gold catalysis through a two-fold intramolecular nucleophilic addition.

Copper-catalyzed coupling of oxime acetates and aryldiazonium salts: an azide-free strategy toward N-2-aryl-1,2,3-triazoles

An azide-free strategy for the synthesis of N-2-aryl-1,2,3-triazoles via copper-catalyzed coupling of oxime acetates and aryldiazonium tetrafluoroborates.

Preparation of pyridyltriazole ruthenium complexes as effective catalysts for the selective alkylation and one-pot C–H hydroxylation of 2-oxindole with alcohols and mechanism exploration

Pyridyltriazole-ligated ruthenium(ii) complexes have been designed and synthesized, which were characterized by X-ray crystallography.

Where does Au coordinate to N-(2-pyridiyl)benzotriazole: gold-catalyzed chemoselective dehydrogenation and borrowing hydrogen reactions

Pyridyltriazole gold(i) complexes proved to be an efficient precatalyst for the most challenging gold-catalyzed borrowing hydrogen reaction and dehydrogenation of alcohols and amines.

Palladium-Catalyzed One-Pot Conversion of Aldehydes and Ketones into 4-Substituted Homopropargyl Alcohols and 5-En-3-yn-1-ols †

Sequential treatment of 2,3-dichloropropene with magnesium and n-BuLi generated the equivalent of 1,3-dilithiopropyne, which adds regiospecifically to aldehydes and ketones to produce homopropargyl alcohols. The lithium acetylide intermediate formed in this protocol can be further reacted with aromatic and vinyl halides, under palladium catalysis, to produce 4-substituted homopropargyl alcohols and 5-en-3-yn-1-ols, respectively, in one-pot with good overall yields.

Gold Redox Catalysis through Base-Initiated Diazonium Decomposition toward Alkene, Alkyne, and Allene Activation

The discovery of photoassisted diazonium activation toward gold(I) oxidation greatly extended the scope of gold redox catalysis by avoiding the use of a strong oxidant. Some practical issues that limit the application of this new type of chemistry are the relative low efficiency (long reaction time and low conversion) and the strict reaction condition control that is necessary (degassing and inert reaction environment). Herein, an alternative photofree condition has been developed through Lewis base induced diazonium activation. With this method, an unreactive AuI catalyst was used in combination with Na2 CO3 and diazonium salts to produce a AuIII intermediate. The efficient activation of various substrates, including alkyne, alkene and allene was achieved, followed by rapid AuIII reductive elimination, which yielded the C-C coupling products with good to excellent yields. Relative to the previously reported photoactivation method, our approach offered greater efficiency and versatility through faster reaction rates and broader reaction scope. Challenging substrates such as electron rich/neutral allenes, which could not be activated under the photoinitiation conditions (<5 % yield), could be activated to subsequently yield the desired coupling products in good to excellent yield.