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Abstract
Thermal isomerizations of various propargyl 3-acylpropiolates are described. Many result in the formation of 3-acylbutenolides. These reactions appear to proceed through intermediate 2,3-dehydropyrans (strained cyclic allenes), which then isomerize in a previously unobserved fashion. Competitive processes that provide additional mechanistic insights are also described.
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52
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Xiao X, Woods BP, Xiu W, Hoye TR. Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity. Angew Chem Int Ed Engl 2018; 57:9901-9905. [PMID: 29874408 PMCID: PMC6296485 DOI: 10.1002/anie.201803872] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2018] [Revised: 05/23/2018] [Indexed: 10/14/2022]
Abstract
The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels-Alder trapping of the BCB by either pendant or external electron-deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three-component process joining the benzyne first with an electron-rich and then with an electron-poor alkyne was uncovered. Reactions in which the BCB functions in a rarely observed role as a 4π diene component in Diels-Alder reactions are reported. The results also shed new light on aspects of the hexadehydro-Diels-Alder reaction used to generate the benzynes.
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53
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Yu X, Jia J, Xu S, Lao KU, Sanford MJ, Ramakrishnan RK, Nazarenko SI, Hoye TR, Coates GW, DiStasio RA. Unraveling substituent effects on the glass transition temperatures of biorenewable polyesters. Nat Commun 2018; 9:2880. [PMID: 30038298 PMCID: PMC6056526 DOI: 10.1038/s41467-018-05269-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 06/14/2018] [Indexed: 11/22/2022] Open
Abstract
Converting biomass-based feedstocks into polymers not only reduces our reliance on fossil fuels, but also furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities. Here we report a series of high glass transition temperature (Tg up to 184 °C) polyesters derived from sugar-based furan derivatives as well as a joint experimental and theoretical study of substituent effects on their thermal properties. Surprisingly, we find that polymers with moderate steric hindrance exhibit the highest Tg values. Through a detailed Ramachandran-type analysis of the rotational flexibility of the polymer backbone, we find that additional steric hindrance does not necessarily increase chain stiffness in these polyesters. We attribute this interesting structure-property relationship to a complex interplay between methyl-induced steric strain and the concerted rotations along the polymer backbone. We believe that our findings provide key insight into the relationship between structure and thermal properties across a range of synthetic polymers.
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54
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Xiao X, Woods BP, Xiu W, Hoye TR. Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201803872] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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55
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McClintock MK, Fahnhorst GW, Hoye TR, Zhang K. Engineering the production of dipicolinic acid in E. coli. Metab Eng 2018; 48:208-217. [DOI: 10.1016/j.ymben.2018.05.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 05/09/2018] [Accepted: 05/16/2018] [Indexed: 10/16/2022]
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56
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Fahnhorst GW, Hoye TR. A Carbomethoxylated Polyvalerolactone from Malic Acid: Synthesis and Divergent Chemical Recycling. ACS Macro Lett 2018; 7:143-147. [PMID: 35610909 DOI: 10.1021/acsmacrolett.7b00889] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report here the synthesis of a novel substituted polyvalerolactone from the renewable monomer, 4-carbomethoxyvalerolactone (CMVL, two steps from malic acid). The polymerization proceeds to high equilibrium monomer conversion to give the semicrystalline carbomethoxylated polyester with low dispersity. The material displays a glass transition temperature of -18 °C and two melting temperatures at 68 and 86 °C. This polymer can be chemically recycled by either of two independent pathways. The first (red) cleanly returns CMVL by a backbiting depolymerization from the hydroxy terminus; the second (blue) uses a base to cleave the polyester in a retro-oxa-Michael fashion. This affords a methacrylate-like monomer that we have polymerized radically to a new polymethacrylate analogue. This is a rare example of a polymer that has been shown to have two independent chemical recycling pathways leading to two different classes of monomers.
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57
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Wang Y, Hoye TR. Intramolecular Capture of HDDA-Derived Benzynes: (i) 6- to 12-Membered Ring Formation, (ii) Internally (vis-à-vis Remotely) Tethered Traps, and (iii) Role of the Rate of Trapping by the Benzynophile. Org Lett 2018; 20:88-91. [PMID: 29244510 DOI: 10.1021/acs.orglett.7b03436] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Reported here are studies that have established novel features of the hexadehydro-Diels-Alder reaction of substrates containing tethered trapping moieties. Products having new structural motifs can be created. (i) Medium-sized fused rings can be produced by varying the length of the tether. (ii) The tether can emanate from an atom within the linker unit that joins the 1,3-diyne and diynophile. (iii) The importance of the rate of trapping by the benzynophile is established.
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58
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Ross SP, Hoye TR. Multiheterocyclic Motifs via Three-Component Reactions of Benzynes, Cyclic Amines, and Protic Nucleophiles. Org Lett 2018; 20:100-103. [PMID: 29239617 PMCID: PMC6344887 DOI: 10.1021/acs.orglett.7b03458] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A broadly general, three-component reaction strategy for the construction of compounds containing multiple heterocycles is described. Thermal benzyne formation (by the hexadehydro-Diels-Alder (HDDA) reaction) in the presence of tertiary cyclic amines and a protic nucleophile (HNu) gives, via ring-opening of intermediate ammonium ion/Nu- ion pairs, heterocyclic products. Many reactions are efficient even when the stoichiometric loading of the three reactants approaches unity. Use of HOSO2CF3 as the HNu gives ammonium triflate intermediates, which can then be ring opened by an even wider variety of nucleophiles.
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59
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Ross SP, Baire B, Hoye TR. Mechanistic Duality in Tertiary Amine Additions to Thermally Generated Hexadehydro-Diels-Alder Benzynes. Org Lett 2017; 19:5705-5708. [PMID: 28981290 PMCID: PMC5650509 DOI: 10.1021/acs.orglett.7b02888] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reported here are studies directed at understanding the mechanism of tertiary amine addition to hexadehydro-Diels-Alder (HDDA)-generated benzynes. Tertiary amines are presumed to engage benzynes by generation of a zwitterionic intermediate. Simple trialkylamines undergo intermolecular protonation by a protic nucleophile to give an aryl ammonium intermediate that is then dealkylated. Amines containing acidified β-protons undergo an intramolecular elimination to give the aniline and an alkene. Finally, amino alcohols react at either of their N- or O atoms, depending upon the extent of internal hydrogen bonding.
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60
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Li K, Scott AM, Brant CO, Fissette SD, Riedy JJ, Hoye TR, Li W. Bile Salt-like Dienones Having a Novel Skeleton or a Rare Substitution Pattern Function as Chemical Cues in Adult Sea Lamprey. Org Lett 2017; 19:4444-4447. [PMID: 28816048 DOI: 10.1021/acs.orglett.7b01921] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Two novel sulfated bile salt-like dienones, featuring either a unique, rearranged side chain or a rare cis-11,12-diol on the steroidal C-ring, herein named petromyzene A (1) and B (2), respectively, were isolated from water conditioned with spawning male sea lamprey (Petromyzon marinus; a jawless vertebrate animal). The structures of these natural products were elucidated by mass spectrometry and NMR spectroscopy. Petromyzenes A and B exhibited high olfactory potency for adult sea lamprey and strong behavioral attraction for spawning females.
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61
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Abstract
We demonstrate that the hexadehydro-Diels-Alder (HDDA) cycloisomerization reaction to produce reactive benzyne derivatives can be initiated photochemically. As with the thermal variant of the HDDA process, the reactive intermediates are formed in the absence of reagents or the resulting byproducts required for the generation of benzynes by traditional methods. This photo-HDDA (or hν-HDDA) reaction occurs at much lower temperatures (including even at -70 °C) than the thermal HDDA, but the benzynes produced behave in the same fashion with respect to their trapping reactions, suggesting they are of the same electronic state.
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62
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Nyongbela KD, Ntie-Kang F, Hoye TR, Efange SMN. Antiparasitic Sesquiterpenes from the Cameroonian Spice Scleria striatinux and Preliminary In Vitro and In Silico DMPK Assessment. NATURAL PRODUCTS AND BIOPROSPECTING 2017; 7:235-247. [PMID: 28421410 PMCID: PMC5481270 DOI: 10.1007/s13659-017-0125-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/25/2016] [Accepted: 03/23/2017] [Indexed: 06/07/2023]
Abstract
The antiparasitic activity and preliminary in vitro and in silico drug metabolism and pharmacokinetic (DMPK) assessment of six isomeric sesquiterpenes (1-6), isolated from the Cameroonian spice Scleria striatinux De Wild (Cyperaceae) is reported. The study was prompted by the observation that two of the compounds (1 and 2) exhibited varying levels of antiparasitic activity on Plasmodium falciparum, Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. The in silico method employed a total of 46 descriptors, calculated using Schrödinger QikProp software. 18 of these molecular descriptors that are often used to predict DMPK profiles of drug-like molecules have been selected for discussion. In vitro experimental assessment of metabolic stability made use of human liver microsomes, which was used to correlate theoretical predictions with experimental findings. Overall, the test compounds have been found to have acceptable physicochemical properties and fall within the ranges associated with "drug-like" molecules. Moreover, the compounds exhibited minimal degradation in incubations with human liver microsomes. Although some of these compounds have been reported previously (1, 2, 4 and 5), this is the first report on their antiparasitic activities, as well as assessment of their DMPK profiles. These results have therefore provided a window for further development of this novel class of sesquiterpene molecules as potential antiparasitic drugs.
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63
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Ross SP, Hoye TR. Reactions of hexadehydro-Diels-Alder benzynes with structurally complex multifunctional natural products. Nat Chem 2017; 9:523-530. [PMID: 28537589 DOI: 10.1038/nchem.2732] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Accepted: 12/30/2016] [Indexed: 11/09/2022]
Abstract
An important question in organic chemistry concerns the extent to which benzynes-one of the classical reactive intermediates in organic chemistry-can react in discriminating fashion with trapping reagents. In particular, whether these species can react selectively with substrates containing multiple functional groups and possible sites of reactivity has remained unanswered. Natural products comprise a palette of multifunctional compounds with which to address this question. Here, we show that benzynes produced by the hexadehydro-Diels-Alder (HDDA) reaction react with many secondary metabolites with a preference for one among several pathways. Examples demonstrating such selectivity include reactions with: phenolics, through dearomatizing ortho-substitution; alkaloids, through Hofmann-type elimination; tropolone and furan, through cycloaddition; and alkaloids, through three-component fragmentation-coupling reactions. We also demonstrate that the cinchona alkaloids quinidine and quinine give rise to products (some in as few as three steps) that enable subsequent and rapid access to structurally diverse polyheterocyclic compounds. The results show that benzynes are quite discriminating in their reactivity-a trait perhaps not broadly enough appreciated.
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64
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Guptill DM, Brutman JP, Hoye TR. Thermoplastic polyurethanes from β-methyl-δ-valerolactone-derived amidodiol chain extenders. POLYMER 2017. [DOI: 10.1016/j.polymer.2017.01.042] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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65
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Palani V, Chen J, Hoye TR. Reactions of Hexadehydro-Diels-Alder (HDDA)-Derived Benzynes with Thioamides: Synthesis of Dihydrobenzothiazino-Heterocyclics. Org Lett 2016; 18:6312-6315. [PMID: 27978648 DOI: 10.1021/acs.orglett.6b03199] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reaction of thioamides (e.g., II) with benzynes generated by the hexadehydro-Diels-Alder (HDDA) cycloisomerization (e.g., I) produces dihydrobenzothiazines (e.g., III). It is postulated that the reaction proceeds via benzothietene (cf. IV) and o-thiolatoaryliminium (cf. V) intermediates and that the latter undergoes intramolecular 1,3-hydrogen atom migration to produce the penultimate isomeric iminium zwitterions VI.
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66
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Xu F, Xiao X, Hoye TR. Reactions of HDDA-Derived Benzynes with Perylenes: Rapid Construction of Polycyclic Aromatic Compounds. Org Lett 2016; 18:5636-5639. [PMID: 27766886 PMCID: PMC5107110 DOI: 10.1021/acs.orglett.6b02878] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Benzynes produced by the thermal cycloisomerization of tetrayne substrates [i.e., by the hexadehydro-Diels-Alder (HDDA) reaction] react with perylenes to produce novel naphthoperylene derivatives. Cyclic voltammetry and absorption and emission properties of these compounds are described. DFT studies shed additional light on the dearomatization that accompanies the reaction as well as some of the spectroscopic behavior.
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67
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Zhang J, Niu D, Brinker VA, Hoye TR. The Phenol-Ene Reaction: Biaryl Synthesis via Trapping Reactions between HDDA-Generated Benzynes and Phenolics. Org Lett 2016; 18:5596-5599. [PMID: 27767316 DOI: 10.1021/acs.orglett.6b02830] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Benzynes produced thermally by the cycloisomerization of triyne-containing precursors [i.e., by the hexadehydro-Diels-Alder (HDDA) reaction] react with phenols at the carbon ortho to the hydroxyl in an enelike fashion. Following tautomerization of the intermediate cyclohexadienones, this produces biaryl derivatives. DFT calculations of model reactions support this mechanistic interpretation. Substituted, unsymmetrical phenols and bis-phenols react in a fashion that can be explained by engagement of the most readily available (non-hydrogen-bonded) hydroxyl in the phenol-ene process.
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68
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Ball-Jones NR, Fahnhorst GW, Hoye TR. Poly(isoprenecarboxylates) from Glucose via Anhydromevalonolactone. ACS Macro Lett 2016; 5:1128-1131. [PMID: 27933217 PMCID: PMC5137944 DOI: 10.1021/acsmacrolett.6b00560] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A short and efficient synthesis of a series of isoprenecarboxylic acid esters (ICAEs) and their corresponding polymers is presented. The base-catalyzed eliminative ring-opening of anhydromevalonolactone (3) provides isoprenecarboxylic acid (6-H), which was further transformed to the ICAEs. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to synthesize high molecular weight (>100 kg mol-1) poly(isoprenecarboxylates) with dispersities (Đ) of ca. 1.5. The glass transition temperatures (Tg) and entanglement molecular weights (Me) of the poly(isoprenecarboxylates) were determined and showed similar trends to the Tg and Me values for analogous poly(acrylate esters). These new glucose-derived materials could provide a sustainable alternative to poly(acrylates).
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69
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Wang T, Hoye TR. Hexadehydro-Diels-Alder (HDDA)-Enabled Carbazolyne Chemistry: Single Step, de Novo Construction of the Pyranocarbazole Core of Alkaloids of the Murraya koenigii (Curry Tree) Family. J Am Chem Soc 2016; 138:13870-13873. [PMID: 27734671 DOI: 10.1021/jacs.6b09628] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Here we report the use of the hexadehydro-Diels-Alder (HDDA) reaction for the de novo construction of a benzenoid ring in fused polycyclic heteroaromatic carbazole (i.e., [2,3]-benzoindole) skeletons. The strategy allows creation of highly substituted benzenoids. We also describe the HDDA-enabled chemical synthesis of the natural product alkaloids mahanimbine and koenidine. Trapping of the intermediate carbazolyne with a conjugated enal, proceeding through formal [2+2] cycloaddition, 4π-electrocyclic ring opening, and 6π-electrocyclic ring-closing events, constitutes a robust method for producing pyranocarbazoles.
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70
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Xu F, Hershey KW, Holmes RJ, Hoye TR. Blue-Emitting Arylalkynyl Naphthalene Derivatives via a Hexadehydro-Diels-Alder Cascade Reaction. J Am Chem Soc 2016; 138:12739-12742. [PMID: 27626808 PMCID: PMC5107111 DOI: 10.1021/jacs.6b07647] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We describe here three alkynyl substituted naphthalenes that display promising luminescence characteristics. Each compound is easily and efficiently synthesized in three steps by capitalizing on the hexadehydro-Diels-Alder (HDDA) cycloisomerization reaction in which an intermediate benzyne is captured by tetraphenylcyclopentadienone, a classical trap for benzyne itself. These compounds luminesce in the deep blue when stimulated either optically (i.e., photoluminescence in both solution and solid films) or electrically [in a light-emitting diode (LED)]. The photophysical properties are relatively insensitive to the electronic nature of the substituents (H, OMe, CO2Me) that define these otherwise identical compounds. Overall, our observations suggest that the twisted nature of the five adjacent aryl groups serves to minimize the intermolecular interaction between core naphthalene units in different sample morphologies. These compounds represent promising leads for the identification of others of value as the emissive component of organic LEDs (OLEDs).
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71
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Wang T, Niu D, Hoye TR. The Hexadehydro-Diels-Alder Cycloisomerization Reaction Proceeds by a Stepwise Mechanism. J Am Chem Soc 2016; 138:7832-5. [PMID: 27266843 DOI: 10.1021/jacs.6b03786] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report here experiments showing that the hexadehydro-Diels-Alder (HDDA) cycloisomerization reaction proceeds in a stepwise manner-i.e., via a diradical intermediate. Judicious use of substituent effects was decisive. We prepared (i) a series of triyne HDDA substrates that differed only in the R group present on the remote terminus of the diynophilic alkyne and (ii) an analogous series of dienophilic alkynes (n-C7H15COC≡CR) for use in classical Diels-Alder (DA) reactions (with 1,3-cyclopentadiene). The R groups were CF3, CHO, COMe/Et, CO2Me, CONMe2/Et2, H, and 1-propynyl. The relative rates of both the HDDA cyclization reactions and the simple DA cycloadditions were measured. The reactivity trends revealed a dramatic difference in the behaviors of the CF3 (slowest HDDA and nearly fastest DA) and 1-propynyl (fastest HDDA and slowest DA) containing members of each series. These differences can be explained by invoking radical-stabilizing energies rather than electron-withdrawing effects as the dominating feature of the HDDA reaction.
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72
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Pehere AD, Xu S, Thompson SK, Hillmyer MA, Hoye TR. Diels-Alder Reactions of Furans with Itaconic Anhydride: Overcoming Unfavorable Thermodynamics. Org Lett 2016; 18:2584-7. [PMID: 27214494 DOI: 10.1021/acs.orglett.6b00929] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Unfavorable thermodynamics often render furans reluctant to engage in high-yielding Diels-Alder (DA) cycloaddition reactions. Here, we report the highly efficient conversion of the biosourced reactants itaconic anhydride (IA) and furfuryl alcohol (FA) to a single DA adduct. The free energy advantages provided by anhydride ring opening and crystal lattice energy of the product overcome the loss of aromaticity of the furanoid diene. Detailed (1)H NMR studies provided valuable insights about relevant kinetic and thermodynamic features.
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73
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Wang T, Naredla RR, Thompson SK, Hoye TR. The pentadehydro-Diels-Alder reaction. Nature 2016; 532:484-8. [PMID: 27088605 PMCID: PMC4877333 DOI: 10.1038/nature17429] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Accepted: 02/12/2016] [Indexed: 11/21/2022]
Abstract
In the classic Diels–Alder (DA) [4+2] cycloaddition reaction1, the overall degree of unsaturation of the 4π (diene) and 2π (dienophile) pairs of reactants dictates the oxidation state of the newly formed six-membered carbocycle. For example, in the classic DA reaction, butadiene and ethylene combine to produce cyclohexene. More recent developments include variants in which the hydrogen atom count in the reactant pair and in the resulting product is reduced by2, for example, four in the tetradehydro-DA (TDDA) and by six in the hexadehydro-DA (HDDA3,4,5,6,7) reactions. Any oxidation state higher than tetradehydro leads to the production of a reactive intermediate that is more highly oxidized than benzene. This significantly increases the power of the overall process because trapping of the benzyne intermediate8,9 can be used to increase the structural complexity of the final product in a controllable and versatile manner. In this manuscript, we report an unprecedented net 4π+2π cycloaddition reaction that generates a different, highly reactive intermediate known as an α,3-dehydrotoluene. This species is at the same oxidation state as a benzyne. Like benzynes, α,3-dehydrotoluenes can be captured by various trapping agents to produce structurally diverse products that are complementary to those arising from the HDDA process. We call this new cycloisomerization reaction a pentadehydro-Diels–Alder (PDDA) reaction—a nomenclature chosen for chemical taxonomic rather than mechanistic reasons. In addition to alkynes, nitriles (RC≡N), although non-participants in aza-HDDA reactions, readily function as the 2π-component in PDDA cyclizations to produce, via trapping of the α,3-(5-aza)dehydrotoluene intermediates, pyridine-containing products.
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74
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Chen J, Palani V, Hoye TR. Reactions of HDDA-Derived Benzynes with Sulfides: Mechanism, Modes, and Three-Component Reactions. J Am Chem Soc 2016; 138:4318-21. [PMID: 27010747 DOI: 10.1021/jacs.6b01025] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report here reactions of alkyl sulfides with benzynes thermally generated by the hexadehydro-Diels-Alder (HDDA) cycloisomerization. The initially produced 1,3-betaine (o-sulfonium/aryl carbanion) undergoes intramolecular proton transfer to generate a more stable S-aryl sulfur ylide. This can react in various manners, including engaging weak acids (HA) in the reaction medium. This can produce transient ion pairs ArSR2(+)A(-) that proceed to the products ArSR + RA. When cyclic sulfides are used, A(-) opens the ring and is incorporated into the product, an outcome that constitutes a versatile, three-component coupling process.
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75
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Nyongbela KD, Makolo FL, Hoye TR, Efange SMN. Isolation and Characterization of Sclerienone C from Scleria striatinux. Nat Prod Commun 2016; 11:5-6. [PMID: 26996004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023] Open
Abstract
Herein, we report the isolation and characterization of sclerienone C, a novel sesquiterpene isolated from the methylene chloride/methanol (1:1) extract of Scleria striatinux that we have deduced to have structure 1. This medicinal spice of Cameroon has been shown to display antimicrobial and antiplasmodial activities. The isolation and purification involved a combination of methods including silica gel column chromatography, Sephadex LH-20, and semi-prep HPLC separations. Structure elucidation was carried-out by means of spectroscopic analysis and comparison with previously isolated sesquiterpene derivatives from the plant.
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