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Special Issue "Alkynes: From Reaction Design to Applications in Organic Synthesis"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (30 December 2018)

Special Issue Editor

Guest Editor
Prof. Dr. Igor V. Alabugin

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, USA
Website | E-Mail
Interests: organic reaction mechanisms; stereoelectronic effects; organic photochemistry; DNA photocleavage; carbon-rich materials; chemistry of alkynes; radical chemistry; cyclizations; cycloaromatizations; cycloadditions

Special Issue Information

Dear Colleagues,

Alkyne functionality represents one of the most valuable building blocks of organic chemistry. Despite its seeming simplicity, it combines many unusual and attractive features. For example, the compact carbon-rich alkyne moiety stores >60 kcal/mol of potential energy. Furthermore, alkynes have the same oxidation state as carbonyl compounds and, hence, via simple addition of nucleophiles, offer a “hidden door” entry into carbonyl chemistry. Due to the presence of two independently addressable π-systems, alkynes can readily form four (and, under certain conditions, up to six) new bonds, lending themselves perfectly to the design of cascade transformations. The recent examples of unusual alkyne transformations include ionic chemistry of neutral hydrocarbons, preparation of radicals without radical initiators, generation of excited states without light, "1,2-dicarbene reactivity" of alkynes in "boomerang" radical processes, selective conversion of alkynes into carbonyl compounds, and full disassembly of the alkyne moiety. With the advent of modern catalytic methods, it seems that new reactions of alkynes are discovered every day.

Recognizing the hidden connections between the fundamental features of alkynes and their rich reactivity is essential for uncovering the full potential of this functionality in organic synthesis. The goal of this Special Issue to is to bring multiple examples of new alkyne reactions under one cover to catalyze cross-pollination of ideas for the future development of alkyne chemistry. This issue will contain contributions that cover all aspects of alkyne structure, reactivity, and applications in organic synthesis.

Prof. Dr. Igor V. Alabugin
Guest Editor

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Keywords

  • alkynes
  • cascade transformations
  • catalysis
  • addition

Published Papers (11 papers)

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Research

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Open AccessArticle
Ring Expansion of Alkylidenecarbenes Derived from Lactams, Lactones, and Thiolactones into Strained Heterocyclic Alkynes: A Theoretical Study
Molecules 2019, 24(3), 593; https://doi.org/10.3390/molecules24030593
Received: 30 December 2018 / Revised: 6 February 2019 / Accepted: 6 February 2019 / Published: 7 February 2019
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Abstract
Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled [...] Read more.
Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of β-lactam- and β-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal double and triple bonds. Furthermore, 2-(1-azacyclobutylidene)carbene was found to be nearly isoenergetic with its ring-expanded isomer, and 1-oxacyclopent-2-yne was notably higher in energy than its precursor carbene. In all other cases, the cycloalkynes were lower in energy than the corresponding carbenes. The transition states for ring-expansion were always lower for the 1,2-carbon shifts than for 1,2-nitrogen or oxygen shifts, but higher than for the 1,2-sulfur shifts. These predictions should be verifiable using carbenes bearing appropriate isotopic labels. Computed vibrational spectra for the carbenes, and their ring-expanded isomers, are presented and could be of value to matrix isolation experiments. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessArticle
TfOH-Promoted Reaction of 2,4-Diaryl-1,1,1-Trifluorobut-3-yn-2-oles with Arenes: Synthesis of 1,3-Diaryl-1-CF3-Indenes and Versatility of the Reaction Mechanisms
Molecules 2018, 23(12), 3079; https://doi.org/10.3390/molecules23123079
Received: 5 November 2018 / Revised: 16 November 2018 / Accepted: 17 November 2018 / Published: 25 November 2018
Cited by 1 | PDF Full-text (33303 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF3-substituted diaryl propargyl alcohols) with arenes in CH2Cl2 afford 1,3-diaryl-1-CF3-indenes in yields up to 84%. This new process for synthesis of such CF3-indenes is complete at room temperature within [...] Read more.
The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF3-substituted diaryl propargyl alcohols) with arenes in CH2Cl2 afford 1,3-diaryl-1-CF3-indenes in yields up to 84%. This new process for synthesis of such CF3-indenes is complete at room temperature within one hour. The synthetic potential, scope, and limitations of this reaction were illustrated by more than 70 examples. The proposed reaction mechanism invokes the formation of highly reactive CF3-propargyl cation intermediates that can be trapped at the two mesomeric positions by the intermolecular nucleophilic attack of an arene partner with a subsequent intramolecular ring closure. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessArticle
Synthesis of Carvone-Derived 1,2,3-Triazoles Study of Their Antioxidant Properties and Interaction with Bovine Serum Albumin
Molecules 2018, 23(11), 2991; https://doi.org/10.3390/molecules23112991
Received: 19 October 2018 / Revised: 13 November 2018 / Accepted: 14 November 2018 / Published: 16 November 2018
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Abstract
Natural L-carvone was utilized as a starting material for an efficient synthesis of some terpenyl-derived 1,2,3-triazoles. Chlorination of carvone, followed by nucleophilic substitution with sodium azide resulted in the preparation of 10-azidocarvone. Subsequent CuAAC click reaction with propargylated derivatives provided an efficient synthetic [...] Read more.
Natural L-carvone was utilized as a starting material for an efficient synthesis of some terpenyl-derived 1,2,3-triazoles. Chlorination of carvone, followed by nucleophilic substitution with sodium azide resulted in the preparation of 10-azidocarvone. Subsequent CuAAC click reaction with propargylated derivatives provided an efficient synthetic route to a set of terpenyl-derived conjugates with increased solubility in water. All investigated compounds exhibit high antioxidant activity, which is comparable with that of vitamin C. It was also found that serum albumin and the terpenyl-1,2,3-triazoles hybrids spontaneously undergo reversible binding driven by hydrophobic interactions, suggesting that serum albumin can transport the target triazoles. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessArticle
Synthesis of Acridines through Alkyne Addition to Diarylamines
Molecules 2018, 23(11), 2867; https://doi.org/10.3390/molecules23112867
Received: 15 October 2018 / Revised: 30 October 2018 / Accepted: 31 October 2018 / Published: 3 November 2018
Cited by 1 | PDF Full-text (654 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A new synthesis of substituted acridines is achieved by palladium-catalyzed addition of terminal acetylenes between the aryl rings of bis(2-bromophenyl)amine. By including a diamine base and elevating the temperature, the reaction pathway favors the formation of acridine over a double Sonogashira reaction to [...] Read more.
A new synthesis of substituted acridines is achieved by palladium-catalyzed addition of terminal acetylenes between the aryl rings of bis(2-bromophenyl)amine. By including a diamine base and elevating the temperature, the reaction pathway favors the formation of acridine over a double Sonogashira reaction to form bis(tolan)amine. This method is demonstrated with several aryl-alkynes and alkyl-alkynes. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessCommunication
Highly Efficient Recyclable Sol Gel Polymer Catalyzed One Pot Difunctionalization of Alkynes
Molecules 2018, 23(8), 1879; https://doi.org/10.3390/molecules23081879
Received: 19 June 2018 / Revised: 23 July 2018 / Accepted: 24 July 2018 / Published: 27 July 2018
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Abstract
Amino-bridged gel polymer P1 was discovered to catalyze alkyne halo-functionalization in excellent yields, regioselectivity, functional group compatibility, and recyclability. We have observed that both aromatic and aliphatic alkynes can be converted to α,α-dihalogenated ketones in the presence of polymer P1 under metal-free conditions [...] Read more.
Amino-bridged gel polymer P1 was discovered to catalyze alkyne halo-functionalization in excellent yields, regioselectivity, functional group compatibility, and recyclability. We have observed that both aromatic and aliphatic alkynes can be converted to α,α-dihalogenated ketones in the presence of polymer P1 under metal-free conditions at room temperature within a short reaction time. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessArticle
Vinylation of a Secondary Amine Core with Calcium Carbide for Efficient Post-Modification and Access to Polymeric Materials
Molecules 2018, 23(3), 648; https://doi.org/10.3390/molecules23030648
Received: 16 February 2018 / Revised: 9 March 2018 / Accepted: 9 March 2018 / Published: 13 March 2018
Cited by 2 | PDF Full-text (1804 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We developed a simple and efficient strategy to access N-vinyl secondary amines of various naturally occurring materials using readily available solid acetylene reagents (calcium carbide, KF, and KOH). Pyrrole, pyrazole, indoles, carbazoles, and diarylamines were successfully vinylated in good yields. Cross-linked and [...] Read more.
We developed a simple and efficient strategy to access N-vinyl secondary amines of various naturally occurring materials using readily available solid acetylene reagents (calcium carbide, KF, and KOH). Pyrrole, pyrazole, indoles, carbazoles, and diarylamines were successfully vinylated in good yields. Cross-linked and linear polymers were synthesized from N-vinyl carbazoles through free radical and cationic polymerization. Post-modification of olanzapine (an antipsychotic drug substance) was successfully performed. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Review

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Open AccessReview
Alkynes as Synthetic Equivalents of Ketones and Aldehydes: A Hidden Entry into Carbonyl Chemistry
Molecules 2019, 24(6), 1036; https://doi.org/10.3390/molecules24061036
Received: 18 February 2019 / Revised: 8 March 2019 / Accepted: 11 March 2019 / Published: 15 March 2019
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Abstract
The high energy packed in alkyne functional group makes alkyne reactions highly thermodynamically favorable and generally irreversible. Furthermore, the presence of two orthogonal π-bonds that can be manipulated separately enables flexible synthetic cascades stemming from alkynes. Behind these “obvious” traits, there are other [...] Read more.
The high energy packed in alkyne functional group makes alkyne reactions highly thermodynamically favorable and generally irreversible. Furthermore, the presence of two orthogonal π-bonds that can be manipulated separately enables flexible synthetic cascades stemming from alkynes. Behind these “obvious” traits, there are other more subtle, often concealed aspects of this functional group’s appeal. This review is focused on yet another interesting but underappreciated alkyne feature: the fact that the CC alkyne unit has the same oxidation state as the -CH2C(O)- unit of a typical carbonyl compound. Thus, “classic carbonyl chemistry” can be accessed through alkynes, and new transformations can be engineered by unmasking the hidden carbonyl nature of alkynes. The goal of this review is to illustrate the advantages of using alkynes as an entry point to carbonyl reactions while highlighting reports from the literature where, sometimes without full appreciation, the concept of using alkynes as a hidden entry into carbonyl chemistry has been applied. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessReview
Preparation and Utility of N-Alkynyl Azoles in Synthesis
Molecules 2019, 24(3), 422; https://doi.org/10.3390/molecules24030422
Received: 21 December 2018 / Revised: 16 January 2019 / Accepted: 22 January 2019 / Published: 24 January 2019
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Abstract
Heteroatom-substituted alkynes have attracted a significant amount of interest in the synthetic community due to the polarized nature of these alkynes and their utility in a wide range of reactions. One specific class of heteroatom-substituted alkynes combines this utility with the presence of [...] Read more.
Heteroatom-substituted alkynes have attracted a significant amount of interest in the synthetic community due to the polarized nature of these alkynes and their utility in a wide range of reactions. One specific class of heteroatom-substituted alkynes combines this utility with the presence of an azole moiety. These N-alkynyl azoles have been known for nearly 50 years, but recently there has been a tremendous increase in the number of reports detailing the synthesis and utility of this class of compound. While much of the chemistry of N-alkynyl azoles mirrors that of the more extensively studied N-alkynyl amides (ynamides), there are notable exceptions. In addition, as azoles are extremely common in natural products and pharmaceuticals, these N-alkynyl azoles have high potential for accessing biologically important compounds. In this review, the literature reports of N-alkynyl azole synthesis, reactions, and uses have been assembled. Collectively, these reports demonstrate the growth in this area and the promise of exploiting N-alkynyl azoles in synthesis. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessReview
Nanographene and Graphene Nanoribbon Synthesis via Alkyne Benzannulations
Molecules 2019, 24(1), 118; https://doi.org/10.3390/molecules24010118
Received: 8 December 2018 / Revised: 24 December 2018 / Accepted: 25 December 2018 / Published: 30 December 2018
Cited by 4 | PDF Full-text (4754 KB) | HTML Full-text | XML Full-text
Abstract
The extension of π-conjugation of polycyclic aromatic hydrocarbons (PAHs) via alkyne benzannulation reactions has become an increasingly utilized tool over the past few years. This short review will highlight recent work of alkyne benzannulations in the context of large nanographene as well as [...] Read more.
The extension of π-conjugation of polycyclic aromatic hydrocarbons (PAHs) via alkyne benzannulation reactions has become an increasingly utilized tool over the past few years. This short review will highlight recent work of alkyne benzannulations in the context of large nanographene as well as graphene nanoribbon synthesis along with a brief discussion of the interesting physical properties these molecules display. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessReview
Recent Synthesis Developments of Organoboron Compounds via Metal-Free Catalytic Borylation of Alkynes and Alkenes
Molecules 2019, 24(1), 101; https://doi.org/10.3390/molecules24010101
Received: 28 October 2018 / Revised: 18 December 2018 / Accepted: 19 December 2018 / Published: 28 December 2018
Cited by 3 | PDF Full-text (5505 KB) | HTML Full-text | XML Full-text
Abstract
Diboron reagents have been traditionally regarded as “Lewis acids”, which can react with simple Lewis base to create a significant nucleophilic character in one of boryl moieties. In particular, bis(pinacolato)diboron (B2pin2) reacts with simple Lewis bases, such as N [...] Read more.
Diboron reagents have been traditionally regarded as “Lewis acids”, which can react with simple Lewis base to create a significant nucleophilic character in one of boryl moieties. In particular, bis(pinacolato)diboron (B2pin2) reacts with simple Lewis bases, such as N-heterocyclic carbenes (NHCs), phosphines and alkoxides. This review focuses on the application of trivalent nucleophilic boryl synthon in the selective preparation of organoboron compounds, mainly through metal-free catalytic diboration and the β-boration reactions of alkynes and alkenes. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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Open AccessReview
Acetylene in Organic Synthesis: Recent Progress and New Uses
Molecules 2018, 23(10), 2442; https://doi.org/10.3390/molecules23102442
Received: 16 August 2018 / Revised: 14 September 2018 / Accepted: 17 September 2018 / Published: 24 September 2018
Cited by 7 | PDF Full-text (68329 KB) | HTML Full-text | XML Full-text
Abstract
Recent progress in the leading synthetic applications of acetylene is discussed from the prospect of rapid development and novel opportunities. A diversity of reactions involving the acetylene molecule to carry out vinylation processes, cross-coupling reactions, synthesis of substituted alkynes, preparation of heterocycles and [...] Read more.
Recent progress in the leading synthetic applications of acetylene is discussed from the prospect of rapid development and novel opportunities. A diversity of reactions involving the acetylene molecule to carry out vinylation processes, cross-coupling reactions, synthesis of substituted alkynes, preparation of heterocycles and the construction of a number of functionalized molecules with different levels of molecular complexity were recently studied. Of particular importance is the utilization of acetylene in the synthesis of pharmaceutical substances and drugs. The increasing interest in acetylene and its involvement in organic transformations highlights a fascinating renaissance of this simplest alkyne molecule. Full article
(This article belongs to the Special Issue Alkynes: From Reaction Design to Applications in Organic Synthesis)
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