Propargylic Alcohols Research Articles

Catalyst-Controlled Divergent Reactions of 2,3-Disubstituted Indoles with Propargylic Alcohols: Synthesis of 3H-Benzo[b]azepines and Axially Chiral Tetrasubstituted Allenes

Catalyst-controlled divergent reactions of 2,3-disubstituted indoles with propargylic alcohols were developed for the first time. In the presence of TsOH or B(C6F5)3 as catalyst, 2,3-disubstituted indoles reacted smoothly with 3-alkynyl-3-hydroxyisoindolinones to afford 3H-benzo[b]azepines by selective C2(sp2)-C3(sp2) ring expansion of indoles. In contrast, decreasing the catalyst strength (e.g., with chiral phosphoric acid) interrupted the cascade reactions, affording axially chiral tetrasubstituted allenes bearing an adjacent chiral quaternary carbon stereocenter. Control experiments provided insights into the reaction mechanism.

Organocatalytic synthesis of chiral allene catalyzed by chiral phosphoric acid via asymmetric 1,8-addition of indole imine methide: Mechanism and origin of enantioselectivity

Organocatalytic synthesis of chiral allene can be successfully achieved through the reaction between propargylic alcohol and 3-phenylindole catalyzed by chiral phosphoric acid with high yield and high enantioselectivity. The detailed reaction mechanism and origin of enantioselectivity were uncovered by quantum mechanical calculations. The results indicate that the reactions undergo the dehydration process, the C–C bonding reaction, the hydrogen abstraction and the regeneration of catalyst. Eight possible pathways were found and the most favorable reaction paths leading to the major and minor products were evaluated which were consistent with the experimental results. The distortion/interaction analyses of the transition states in enantioselectivity-determining steps confirm the most favorable pathway in leading the major product. QTAIM and IGM analyses are used to illustrate the role of intermolecular interactions. EDA analysis is also employed to understand the origin of selectivity. This work would provide insightful viewpoints on the asymmetric organocatalytic reaction by chiral phosphoric acid.

Engineering noble-metal-free metal–organic framework composite catalyst for efficient CO2 conversion under ambient conditions

The cyclization of propargylic alcohols and propargylic amines with CO2 are of great significance since the generated O/N-containing cyclic skeletons are extensively employed in pharmaceutical chemistry and industrial production. However, most of the reported catalysts only effectively catalyze propargylic alcohols or propargylic amines with CO2, and often involve noble-metal catalysts, high temperature and CO2 pressure. It is a great challenge that non-noble-metal catalysts catalyzed both propargylic alcohols and propargylic amines with CO2 under ambient conditions. Herein, CuBr@NH2-MIL-101 was successfully synthesized by loading CuBr nanoparticles into zeolite-type NH2-MIL-101 via simple thermal conversion method, and it displayed highly selective CO2 uptake properties. Importantly, CuBr@NH2-MIL-101 featured high catalytic activity for carboxylative cyclization of both propargylic alcohols and propargylic amines with CO2 under ambient conditions (25 °C, 0.1 MPa CO2), respectively. Moreover, CuBr@NH2-MIL-101 can be recycled at least three times without significant decline in catalytic activity. The combination explorations of NMR, FTIR and 13C isotope labeling experiments clearly illustrate the reaction process and mechanism. The density functional theory (DFT) calculations uncover that CuBr and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) can synergistically activate substrates, and the proton-demetalation step with the highest energy barrier was the rate-determining step in two catalytic systems. To our knowledge, it is the first report of noble-metal-free catalyst that can simultaneously catalyze CO2 conversion with propargylic alcohols and propargylic amines under room temperature and atmospheric CO2 pressure.

Metal-Free, Adjustable, and Recyclable Catalytic Systems for the Construction of C–C Bonds by Activating Propargylic Alcohols

Pyrano[3,2-c]coumarin derivatives and C3-substituted 4-hydroxycoumarins as important skeletal structures of active natural products and pharmaceutically relevant molecules have received increasing attention. However, developing an adjustable system for selectively synthesizing them is still a challenging task. Herein, sulfonic acid-functionalized ionic liquid was successfully used as the catalyst for the alkylation of 4-hydroxycoumarin derivatives with secondary aromatic propargylic alcohols using dimethyl carbonate as the green solvent, giving up to 98% yield. On the other hand, protonated imidazole-based ionic liquid-catalyzed cyclization was also selectively achieved with a nearly quantitative yield. Developed metal-free catalytic systems exhibited well adjustable and recyclable properties, avoiding the contamination of metal and halogen, reducing the neutralization after the reaction, and benefiting the separation between the catalyst and the product. New strategies were applied for performing the gram-scale reaction smoothly. The adjustable systems might occur through two different mechanisms involving propargylic or allenic carbocation and hydrogen bonding effects between the catalysts and the substrates.

Acyclic Remote 1,6-Stereoselection.

Stereochemical communication in homopropargylation and homoallylation of aldehydes was achieved by the Ti-O temporary linker strategy. Propargylic and allylic alcohol derivatives were employed as convenient pronucleophiles, obviating prefabrication of propargylation/allylation reagents. It was surprising that 1,6-diastereoselectivity was affected by not only the Grignard reagent but also the reaction solvent.

Silver-anchored porous aromatic framework for efficient conversion of propargylic alcohols with CO2 at ambient pressure

The conversion of propargylic alcohols and carbon dioxide (CO2) into fine chemicals suffers from issues of harsh reaction conditions and difficult catalyst recovery. To achieve efficient CO2 activation at low energy consumption, a silver-anchored porous aromatic framework catalyst Ag@PAF-DAB with high active phase density and CO2 adsorption capacity was proposed. Since Ag@PAF-DAB has the dual functions of CO2 capture and conversion, propargylic alcohols were completely converted into α-alkylidene cyclic carbonate or α‑hydroxy ketone as high value-added product under atmospheric pressure (CO2, 0.1 MPa) and low silver equivalent (0.5 mol%). Notably, Ag@PAF-DAB exhibited broad substrate diversity, high stability, and excellent reusability. By applying FTIR and GC, the key to green synthetic route of α‑hydroxy ketone was confirmed to lie in the further hydration of α-alkylidene cyclic carbonate.

Organocatalytic Asymmetric 3‐Allenylation of Indoles via Remote Stereocontrolled 1,10‐Additions of Alkynyl Indole Imine Methides

AbstractA chiral phosphoric acids catalyzed regio‐ and enantioselective 1,10‐conjugate addition of 2‐arylindoles to alkynyl indole imine methides formed in situ from α‐(6‐indolyl)propargylic alcohols has been developed. With the established system, organocatalytic asymmetric 3‐allenylation of indoles was realized, affording a broad scope of axially chiral tetrasubstituted allenes bearing two indole motifs in high yields with stereoselectivities. Importantly, the organocatalytic remote stereocontrolled strategy disclosed the asymmetric 3‐allenylation of indoles via 1,10‐conjugate addition for the first time.

Insight into the cation-regulated mechanism for the hydration of propargyl alcohols catalyzed by [Bu4P+][Im−

Hydration of propargylic alcohols is one of the most important pathways to synthesize α-hydroxy ketones. However, its mechanism is still obscure in the presence of multiple catalytic species. The mechanism of catalysis for the hydration of propargylic alcohols in the presence of [Bu4P+][Im-] is investigated along with the carbon dioxide (CO2) as the co-catalyst by the density functional theory (DFT) with the aim to elucidate the role of [Bu4P+] cation and [Im-] anion. The CO2 could be absorbed by the [Bu4P+] cation to form [Bu4P-H-CO2] complex after the hydrogen atom in [Bu4P+] cation transfers to the [Im-] anion. Then, both [Bu4P-H-CO2] and [Im+H] are employed as the actual catalytic species to construct a new pathway. It is the more favorable as compared with the previously reported pathways. In previous reported pathway, the [Im-] anion is regarded as the real catalytic species, while [Bu4P+] cation plays the auxiliary role to stabilize the substrate by the hydrogen bond. The mechanism of the same reaction catalyzed by other four different ionic liquids is also investigated to further testify the contribution of [Bu4P+] cation and [Im-] anion in the catalysis. This work not only provides a new insight into the cation-regulated pathway for the hydration of propargylic alcohols but also points out a new strategy to design the ionic liquids achieving the improved catalytic efficiency.

A Sphingolipid Fatty Acid Constituent Made by Alkyne trans‐Hydrogenation: Total Synthesis of Symbioramide

AbstractA scalable approach to (2R)‐hydroxyoctadec‐3‐enoic acid ((−)‐2) is reported, which is the fatty acid constituent of numerous sphingolipids of biological significance. Key to success was the chemoselective trans‐hydrogenation of a functionalized propargylic alcohol precursor with [Cp*RuCl]4 as the catalyst, followed by lipase‐catalyzed resolution of the racemic product. (−)‐2 then served the shortest total synthesis of the marine natural product symbioramide known to date.magnified image

Gold(I)-Catalyzed Synthesis of Heterocycles via Allene Oxide from Propargylic Alcohols.

A new mechanistic pathway of propargylic alcohol activation by gold(I) catalysis has been proposed toward the efficient synthesis of N-protected pyrroles, 5,6-dihydropyridin-3(4H)-ones from N-protected 5-aminopent-2-yn-1-ol, and 5-aminopent-2-yn-1-ol. Control experiments support that the reaction proceeded via the neighboring group participation of the oxygen atom of propargylic alcohol to form an allene oxide intermediate where the nucleophilic heteroatom attacks intramolecularly. Further, this methodology is successfully extrapolated toward the atom-economic synthesis of hydroxyalkyl indoles and benzofurans. The short reaction time of 30 s, low catalyst loading of 0.5 mol %, high yield, variation in the substrate scope, and procedurally simple open-flask reaction conditions make this methodology highly applied.

Ag Nanoparticles Anchored on Nanotubular Porous Porphyrin Networks for Carboxylative Cyclization of Propargyl Alcohols with CO2

AbstractA nanotubular porous porphyrin‐based network (NT‐PPN) was prepared through Friedel–Crafts alkylation polyreaction of meso‐tetraphenylporphyrin iron chloride and subsequent demetalization reaction with concentrated hydrochloric acid. As a superior support, NT‐PPN was decorated with Ag nanoparticles to generate the desired catalyst (Ag@NT‐PPN). Ag@NT‐PPN had a high BET surface area with plentiful hierarchical porosity, considerable CO2 adsorption uptake, as well as high CO2/N2 adsorption selectivity. In the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), Ag@NT‐PPN exhibited excellent catalytic performance for the solvent‐free synthesis of α‐alkylidene cyclic carbonates from propargyl alcohols and CO2 at 30 °C. Ag@NT‐PPN also displayed robust constancy, excellent recyclability, and acceptable substrate expansibility for this reaction. Moreover, low concentration of CO2 derived from mixed gas (15% CO2+85% N2 in volume) was positively amenable to this catalytic protocol. This work might offer an opportunity to design metal NPs‐based heterogeneous catalysts and provide a promising candidate for application in the transformation of CO2 into valuable cyclic carbonates.

Cycloaddition of Propargylic Alcohols and Amines to Carbon Dioxide On Supported Cu2O Nanoparticles

Cycloaddition of Propargylic Alcohols and Amines to Carbon Dioxide On Supported Cu2O Nanoparticles

Silyl-Osmium(IV)-Trihydride Complexes Stabilized by a Pincer Ether-Diphosphine: Formation and Reactions with Alkynes.

Complex OsH4{κ3-P,O,P-[xant(PiPr2)2]} (1) activates the Si-H bond of triethylsilane, triphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane to give the silyl-osmium(IV)-trihydride derivatives OsH3(SiR3){κ3-P,O,P-[xant(PiPr2)2]} [SiR3 = SiEt3 (2), SiPh3 (3), SiMe(OSiMe3)2 (4)] and H2. The activation takes place via an unsaturated tetrahydride intermediate, resulting from the dissociation of the oxygen atom of the pincer ligand 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(PiPr2)2). This intermediate, which has been trapped to form OsH4{κ2-P,P-[xant(PiPr2)2]}(PiPr3) (5), coordinates the Si-H bond of the silanes to subsequently undergo a homolytic cleavage. Kinetics of the reaction along with the observed primary isotope effect demonstrates that the Si-H rupture is the rate-determining step of the activation. Complex 2 reacts with 1,1-diphenyl-2-propyn-1-ol and 1-phenyl-1-propyne. The reaction with the former affords Os{C≡CC(OH)Ph2}2{=C=CHC(OH)Ph2}{κ3-P,O,P-[xant(PiPr2)2]} (6), which catalyzes the conversion of the propargylic alcohol into (E)-2-(5,5-diphenylfuran-2(5H)-ylidene)-1,1-diphenylethan-1-ol, via (Z)-enynediol. In methanol, the hydroxyvinylidene ligand of 6 dehydrates to allenylidene, generating Os{C≡CC(OH)Ph2}2{=C=C=CPh2}{κ3-P,O,P-[xant(PiPr2)2]} (7). The reaction of 2 with 1-phenyl-1-propyne leads to OsH{κ1-C,η2-[C6H4CH2CH=CH2]}{κ3-P,O,P-[xant(PiPr2)2]} (8) and PhCH2CH=CH(SiEt3).

Rhodium-Catalyzed Coordination-Assisted Regioselective and Migratory Three-Point Double Annulation of o-Alkenyl Phenols with Tertiary Propargyl Alcohols.

We disclose herein a Rh(III)-catalyzed migratory three-point double annulation of o-alkenyl phenols with propargyl alcohols for de novo construction of naphtho furan derivatives in a regio- and chemoselective manner. The protocol orchestrates two new rings with four new bonds in one operation without the need for any additive. Necessary labeled and control experiments are conducted to elucidate the reaction mechanism. A tertiary hydroxyl group is found to be crucial both for controlling the regioselective insertion of alkyne through chelation with rhodium to form a key spiro cyclic intermediate and for forcing ring expansion via unusual and selective olefin reshuffling, apart from forming an extra (furan) ring. The protocol is scalable and shows tolerance for late stage functionalization of natural products.

Fe-Catalyzed Selective Formal Insertion of Diazo Compounds into C(sp)-C(sp3) Bonds of Propargyl Alcohols: Access to Alkyne-Substituted All-Carbon Quaternary Centers.

The construction of all-carbon quaternary centers, especially those containing an alkyne-substituted framework, represents an important challenge in organic synthesis. Here we present a novel Fe-catalyzed selective formal insertion of diazo compounds into C(sp)–C(sp3) bonds of propargyl alcohols under mild conditions that enables the streamlined construction of alkyne-substituted all-carbon quaternary centers. This unique strategy starts with in situ generation of an ester group in the presence of carboxylic acids, followed by insertion of metal-carbene into C(sp)–C(sp3) bonds, which may open up a new reaction mode for exploring metal-carbene insertion into acyclic C–C bonds.

Total Synthesis and Biological Evaluation of Mutolide and Analogues.

The convergent total syntheses of three 14-membered macrolide natural products, mutolide, nigrosporolide and (4S,7S,13S)-4,7-dihydroxy-13-tetradeca-2,5,8-trienolide have been achieved. The key synthetic features include Shiina macrolactonization to assemble the 14-membered macrocyclic core, Wittig or Still-Gennari olefination and selective reduction of propargylic alcohol to construct the E- or Z-olefins. Cross metathesis was also highlighted as an efficient tool to forge the formation of E-olefin. The three synthetic macrolides were evaluated for their cytotoxic activity against three human cancer cell lines as well as for inhibitory effect on CFTR-mediated chloride secretion in human intestinal epithelial (T84) cells. Mutolide displayed significant cytotoxic activity against HCT116 colon cancer cells with an IC50 of ∼12 μM as well as a potent CTFR inhibitory effect with an IC50 value of ∼1 μM.

Organocatalytic Enantioselective 1,10-Addition of Alkynyl Indole Imine Methides with Thiazolones: An Access to Axially Chiral Tetrasubstituted Allenes.

An asymmetric organocatalytic remote 1,10-addition of alkynyl indole imine methides generated in situ from α-(6-indolyl) propargylic alcohols with thiazolones has been developed for the first time, affording axially chiral tetrasubstituted allenes featuring vicinal sulfur-containing quaternary carbon stereocenters in high yields with excellent stereoselectivities. The representative scale-up reaction and transformations of the 1,10-adduct were examined. The reaction mechanism was expounded by control experiments and DFT calculations.

Hydrogenation of alkynyl ketones catalyzed by tetrabutylammonium bromide

<p indent="0mm">Propargyl alcohol compounds have many applications in medicine, pesticides and functional molecular materials, and are also important intermediates in organic synthesis because they contain alkynyl and hydroxyl groups in the molecules. The common preparation methods for propargyl alcohol usually rely on the transition metal catalyzed hydrogenation reaction and the alkynylation of ketones, which is high cost and with poor tolerance of the substitution groups. In this article, the hydrogenation reaction of alkynyl ketones with pinacolborane was developed with tetrabutylammonium bromide as catalyst. The present method provided a convenient, economical and efficient method for the synthesis of propargyl alcohol compounds.

Some aspects of the mechanism of steel protection in hydrochloric acid solutions by propargyl alcohol

Some aspects of the mechanism of steel protection in hydrochloric acid solutions by propargyl alcohol

Regioselective Cycloaddition and Substitution Reaction of Tertiary Propargylic Alcohols and Heteroareneboronic Acids via Acid Catalysis.

We report an acid-catalyzed formal cycloaddition and dehydrative substitution reaction of tertiary propargylic alcohols and heteroareneboronic acids. The properties of the substituents on the alkynyl moiety determines the regioselectivity of the reaction, which could selectively construct fused heterocycles, tetrasubstituted allenes, or 1,3-dienes. This reaction proceeds efficiently with a wide array of substrate scope in up to 89% yield. A significant advantage of this protocol is the transition-metal-free and mild conditions needed.