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Alois Furstner - One of the best experts on this subject based on the ideXlab platform.
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Hydroxyl-Assisted trans-Reduction of 1,3-Enynes: Application to the Formal Synthesis of (+)-Aspicilin
Synthesis, 2016Co-Authors: Sebastian Schaubach, Kenichi Michigami, Alois FurstnerAbstract:1,3-Enynes are hardly amenable to trans-hydrometalation reactions, because they tend to bind the standard ruthenium catalysts too tightly. However, catalysts comprising a [Cp*Ru–Cl] unit allow such compounds to be used, provided they contain an OH group next to the triple bond. This aspect is illustrated by a formal synthesis of the lichen-derived macrolide aspicilin. The required macrocyclic Enyne precursor was formed by an efficient ring-closing alkyne metathesis reaction.
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e cycloalkenes and e e cycloalkadienes by ring closing diyne or Enyne yne metathesis semi reduction
Tetrahedron, 2004Co-Authors: Fabrice Lacombe, Karin Radkowski, Gunter Seidel, Alois FurstnerAbstract:Abstract A concise, practical and stereoselective entry into macrocyclic (E)-alkenes is outlined comprising a sequence of ring closing alkyne metathesis (RCAM), trans-selective hydrosilylation of the resulting cycloalkynes catalyzed by [Cp∗Ru(MeCN)3]PF6, and a protodesilylation of the ensuing vinylsilanes with AgF in aq. THF/MeOH. Moreover, the first examples of intramolecular Enyne–yne metathesis reactions catalyzed by the Schrock alkylidyne complex (tBuO)3WCCMe3 are reported; the resulting cyclic Enynes can be converted along similar lines into the corresponding (E,E)-configured 1,3-dienes in good overall yields. Cycloalkyne 4 and the (E)-configured cyclic olefins 6 and 21 were characterized by X-ray crystallography.
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platinum catalyzed cycloisomerization reactions of Enynes
Journal of the American Chemical Society, 2001Co-Authors: Alois Furstner, Frank Stelzer, Hauke SzillatAbstract:PtCl2 constitutes an efficient and practical catalyst for a set of different atom economical rearrangement reactions of Enynes. This includes (i) a formal Enyne metathesis reaction delivering 1,3-dienes, (ii) the formation of polycyclic vinylcyclopropane derivatives, and (iii) an unprecedented O→C allyl shift reaction if unsaturated ethers are employed. Although these transformations produce significantly different structural motifs, they share a common mechanism comprising a cationic manifold triggered by the π-complexation of Pt(II) onto the alkyne unit of the substrates. Strong experimental support for the proposed mechanism comes from deuterium-labeling studies, a careful analysis of the product distribution pattern, and the fact that in some cases PtCl2 can be replaced by simple Lewis or Bronsted acids as the catalysts.
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platinum and acid catalyzed Enyne metathesis reactions mechanistic studies and applications to the syntheses of streptorubin b and metacycloprodigiosin
Journal of the American Chemical Society, 1998Co-Authors: Alois Furstner, Hauke Szillat, Barbara Gabor, Richard MynottAbstract:Formal total syntheses of the antibiotics metacycloprodigiosin (2) and streptorubin B (3) are described, which are known to exhibit promising immunomodulating properties. The key step en route to their meta-bridged pyrrole core structures 5 and 7, respectively, consists of a metathesis reaction of electron-deficient Enynes catalyzed by either platinum halides, hard Lewis acids, or HBF4. This transformation expands the pre-existing cycloalkene of the substrates by two C atoms, forges the bicyclic pyrrolophane structure of the targets, and simultaneously forms a bridgehead alkene function. The products of this skeletal rearrangement are converted into the targets by a sequence comprising (i) a stepwise reduction of their enone entity to the corresponding saturated alcohols and (ii) an aromatization of the N-tosylated dihydropyrroles 20 and 34 thus obtained via elimination of potassium sulfinate on exposure to KAPA (potassium 3-aminopropylamide). A careful analysis of the minor byproducts formed in the Enyne...
Amir H. Hoveyda - One of the best experts on this subject based on the ideXlab platform.
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enantioselective synthesis of trisubstituted allenyl b pin compounds by phosphine cu catalyzed 1 3 Enyne hydroboration insights regarding stereochemical integrity of cu allenyl intermediates
Journal of the American Chemical Society, 2018Co-Authors: Youming Huang, Juan Del Pozo, Sebastian Torker, Amir H. HoveydaAbstract:Catalytic enantioselective boron-hydride additions to 1,3-Enynes, which afford allenyl-B(pin) (pin = pinacolato) products, are disclosed. Transformations are promoted by a readily accessible bis-phosphine-Cu complex and involve commercially available HB(pin). The method is applicable to aryl- and alkyl-substituted 1,3-Enynes. Trisubstituted allenyl-B(pin) products were generated in 52-80% yield and, in most cases, in >98:2 allenyl:propargyl and 92:8-99:1 enantiomeric ratio. Utility is highlighted through a highly diastereoselective addition to an aldehyde, and a stereospecific catalytic cross-coupling process that delivers an enantiomerically enriched allene with three carbon-based substituents. The following key mechanistic attributes are elucidated: (1) Spectroscopic and computational investigations indicate that low enantioselectivity can arise from loss of kinetic stereoselectivity, which, as suggested by experimental evidence, may occur by formation of a propargylic anion generated by heterolytic Cu-C cleavage. This is particularly a problem when trapping of the Cu-allenyl intermediate is slow, namely, when an electron deficient 1,3-Enyne or a less reactive boron-hydride reagent (e.g., HB(dan) (dan = naphthalene-1,8-diaminato)) is used or under non-optimal conditions (e.g., lower boron-hydride concentration causing slower trapping). (2) With Enynes that contain a sterically demanding o-aryl substituent considerable amounts of the propargyl-B(pin) isomer may be generated (25-96%) because a less sterically demanding transition state for Cu/B exchange becomes favorable. (3) The phosphine ligand can promote isomerization of the enantiomerically enriched allenyl-B(pin) product; accordingly, lower ligand loading might at times be optimal. (4) Catalytic cross-coupling with an enantiomerically enriched allenyl-B(pin) compound might proceed with high stereospecificity (e.g., phosphine-Pd-catalyzed cross-coupling) or lead to considerable racemization (e.g., phosphine-Cu-catalyzed allylic substitution).
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Enantioselective Synthesis of Trisubstituted Allenyl–B(pin) Compounds by Phosphine–Cu-Catalyzed 1,3-Enyne Hydroboration. Insights Regarding Stereochemical Integrity of Cu–Allenyl Intermediates
2018Co-Authors: Youming Huang, Juan Del Pozo, Sebastian Torker, Amir H. HoveydaAbstract:Catalytic enantioselective boron–hydride additions to 1,3-Enynes, which afford allenyl–B(pin) (pin = pinacolato) products, are disclosed. Transformations are promoted by a readily accessible bis-phosphine–Cu complex and involve commercially available HB(pin). The method is applicable to aryl- and alkyl-substituted 1,3-Enynes. Trisubstituted allenyl–B(pin) products were generated in 52–80% yield and, in most cases, in >98:2 allenyl:propargyl and 92:8–99:1 enantiomeric ratio. Utility is highlighted through a highly diastereoselective addition to an aldehyde, and a stereospecific catalytic cross-coupling process that delivers an enantiomerically enriched allene with three carbon-based substituents. The following key mechanistic attributes are elucidated: (1) Spectroscopic and computational investigations indicate that low enantioselectivity can arise from loss of kinetic stereoselectivity, which, as suggested by experimental evidence, may occur by formation of a propargylic anion generated by heterolytic Cu–C cleavage. This is particularly a problem when trapping of the Cu–allenyl intermediate is slow, namely, when an electron deficient 1,3-Enyne or a less reactive boron–hydride reagent (e.g., HB(dan) (dan = naphthalene-1,8-diaminato)) is used or under non-optimal conditions (e.g., lower boron–hydride concentration causing slower trapping). (2) With Enynes that contain a sterically demanding o-aryl substituent considerable amounts of the propargyl–B(pin) isomer may be generated (25–96%) because a less sterically demanding transition state for Cu/B exchange becomes favorable. (3) The phosphine ligand can promote isomerization of the enantiomerically enriched allenyl–B(pin) product; accordingly, lower ligand loading might at times be optimal. (4) Catalytic cross-coupling with an enantiomerically enriched allenyl–B(pin) compound might proceed with high stereospecificity (e.g., phosphine–Pd-catalyzed cross-coupling) or lead to considerable racemization (e.g., phosphine–Cu-catalyzed allylic substitution)
Michael Schmittel - One of the best experts on this subject based on the ideXlab platform.
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the photochemical c2 c6 cyclization of Enyne allenes interception of the fulvene diradical with a radical clock ring opening
Journal of Organic Chemistry, 2009Co-Authors: Gotz Bucher, Atul A Mahajan, Michael SchmittelAbstract:The mechanism of the photochemical C(2)-C(6) cyclization of Enyne-allenes has been studied through radical clock, intramolecular kinetic isotope effect, and laser flash photolysis (LFP) experiments as well as density functional theory (DFT) and ab initio computations. While the photochemical cyclization of Enyne-allenes 1 and 2 furnished ene and Diels-Alder products without any cyclopropyl ring opening, that of 3 carrying the ultrafast diphenylcyclopropylcarbinyl radical clock afforded products derived from cyclopropyl ring opening. Laser flash photolysis (LFP) studies on Enyne-allene 3 point to an allene triplet excited state (transient A) as a primarily formed short-lived (tau = 430 ns) intermediate. In addition, we have obtained evidence for the formation of a diphenylmethyl-type diradical (transient C, tau = 1.0 micros) resulting from ring opening of a diphenylcyclopropane ring. C subsequently undergoes a surprisingly slow (tau = 1.0 micros) 1,6-hydrogen shift leading to the stable 1,3-diene 6.
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photochemical c2 c6 cyclization of Enyne allenes detection of a fulvene triplet diradical in the laser flash photolysis
Journal of Organic Chemistry, 2008Co-Authors: Gotz Bucher, Atul A Mahajan, Michael SchmittelAbstract:A series of Enyne−allenes, with and without benzannulation at the ene moiety and equipped with aromatic and carbonyl groups as internal triplet sensitizer units at the allene terminus, was synthesized. Both sets, the cyclohexEnyne−allenes and benzEnyne−allenes, underwent thermal C2−C6 cyclization exclusively to formal ene products. In contrast, the photochemical C2−C6 cyclization of Enyne−allenes provided formal Diels−Alder and/or ene products, with higher yields for the benzannulated systems. A raise of the temperature in the photochemical cyclization of Enyne−allene 1b′ led to increasing amounts of the ene product in relation to that of the formal Diels−Alder product. Laser flash photolysis at 266 and 355 nm as well as triplet quenching studies for 1b,b′ indicated that the C2−C6 cyclization proceeds via the triplet manifold. On the basis of a density functional theory (DFT) study, a short-lived transient (τ = 30 ns) was assigned as a triplet allene, while a long-lived transient (τ = 33 μs) insensitive t...
Youming Huang - One of the best experts on this subject based on the ideXlab platform.
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enantioselective synthesis of trisubstituted allenyl b pin compounds by phosphine cu catalyzed 1 3 Enyne hydroboration insights regarding stereochemical integrity of cu allenyl intermediates
Journal of the American Chemical Society, 2018Co-Authors: Youming Huang, Juan Del Pozo, Sebastian Torker, Amir H. HoveydaAbstract:Catalytic enantioselective boron-hydride additions to 1,3-Enynes, which afford allenyl-B(pin) (pin = pinacolato) products, are disclosed. Transformations are promoted by a readily accessible bis-phosphine-Cu complex and involve commercially available HB(pin). The method is applicable to aryl- and alkyl-substituted 1,3-Enynes. Trisubstituted allenyl-B(pin) products were generated in 52-80% yield and, in most cases, in >98:2 allenyl:propargyl and 92:8-99:1 enantiomeric ratio. Utility is highlighted through a highly diastereoselective addition to an aldehyde, and a stereospecific catalytic cross-coupling process that delivers an enantiomerically enriched allene with three carbon-based substituents. The following key mechanistic attributes are elucidated: (1) Spectroscopic and computational investigations indicate that low enantioselectivity can arise from loss of kinetic stereoselectivity, which, as suggested by experimental evidence, may occur by formation of a propargylic anion generated by heterolytic Cu-C cleavage. This is particularly a problem when trapping of the Cu-allenyl intermediate is slow, namely, when an electron deficient 1,3-Enyne or a less reactive boron-hydride reagent (e.g., HB(dan) (dan = naphthalene-1,8-diaminato)) is used or under non-optimal conditions (e.g., lower boron-hydride concentration causing slower trapping). (2) With Enynes that contain a sterically demanding o-aryl substituent considerable amounts of the propargyl-B(pin) isomer may be generated (25-96%) because a less sterically demanding transition state for Cu/B exchange becomes favorable. (3) The phosphine ligand can promote isomerization of the enantiomerically enriched allenyl-B(pin) product; accordingly, lower ligand loading might at times be optimal. (4) Catalytic cross-coupling with an enantiomerically enriched allenyl-B(pin) compound might proceed with high stereospecificity (e.g., phosphine-Pd-catalyzed cross-coupling) or lead to considerable racemization (e.g., phosphine-Cu-catalyzed allylic substitution).
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Enantioselective Synthesis of Trisubstituted Allenyl–B(pin) Compounds by Phosphine–Cu-Catalyzed 1,3-Enyne Hydroboration. Insights Regarding Stereochemical Integrity of Cu–Allenyl Intermediates
2018Co-Authors: Youming Huang, Juan Del Pozo, Sebastian Torker, Amir H. HoveydaAbstract:Catalytic enantioselective boron–hydride additions to 1,3-Enynes, which afford allenyl–B(pin) (pin = pinacolato) products, are disclosed. Transformations are promoted by a readily accessible bis-phosphine–Cu complex and involve commercially available HB(pin). The method is applicable to aryl- and alkyl-substituted 1,3-Enynes. Trisubstituted allenyl–B(pin) products were generated in 52–80% yield and, in most cases, in >98:2 allenyl:propargyl and 92:8–99:1 enantiomeric ratio. Utility is highlighted through a highly diastereoselective addition to an aldehyde, and a stereospecific catalytic cross-coupling process that delivers an enantiomerically enriched allene with three carbon-based substituents. The following key mechanistic attributes are elucidated: (1) Spectroscopic and computational investigations indicate that low enantioselectivity can arise from loss of kinetic stereoselectivity, which, as suggested by experimental evidence, may occur by formation of a propargylic anion generated by heterolytic Cu–C cleavage. This is particularly a problem when trapping of the Cu–allenyl intermediate is slow, namely, when an electron deficient 1,3-Enyne or a less reactive boron–hydride reagent (e.g., HB(dan) (dan = naphthalene-1,8-diaminato)) is used or under non-optimal conditions (e.g., lower boron–hydride concentration causing slower trapping). (2) With Enynes that contain a sterically demanding o-aryl substituent considerable amounts of the propargyl–B(pin) isomer may be generated (25–96%) because a less sterically demanding transition state for Cu/B exchange becomes favorable. (3) The phosphine ligand can promote isomerization of the enantiomerically enriched allenyl–B(pin) product; accordingly, lower ligand loading might at times be optimal. (4) Catalytic cross-coupling with an enantiomerically enriched allenyl–B(pin) compound might proceed with high stereospecificity (e.g., phosphine–Pd-catalyzed cross-coupling) or lead to considerable racemization (e.g., phosphine–Cu-catalyzed allylic substitution)
Yue Wang - One of the best experts on this subject based on the ideXlab platform.
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π conjugated aromatic Enynes as a single emitting component for white electroluminescence
Journal of the American Chemical Society, 2006Co-Authors: Masayoshi Nishiura, Yue WangAbstract:By use of the organolanthanide catalysts Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) and (C5Me5)2LaCH(SiMe3)2, carbazole-substituted phenyl Enynes (Z)-CPEY and (E)-CPEY were synthesized, respectively, with excellent regio- and stereoselectivity through the catalytic dimerization of the corresponding terminal alkyne. These new π-conjugated compounds, in particular, the (E)-Enyne isomer (E)-CPEY, act as an excellent single-emitting component for white organic light-emitting devices (WOLEDs), as a result of combination of the blue emission from an isolated molecule with the longer-wavelength emissions (green and orange-red) from excimers. The (E)-CPEY-based double-layer device emitted almost pure white light with CIE coordinates of (0.32, 0.33), maximum brightness of 1395 cd m-2, and maximum current efficiency of 2.07 cd A-1. This is perhaps the purest white emission ever reported for a single-emitting-component WOLED. The quality of the white emission remained almost unchanged under varying driving voltages, demonst...
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π conjugated aromatic Enynes as a single emitting component for white electroluminescence
Journal of the American Chemical Society, 2006Co-Authors: Yu Liu, Masayoshi Nishiura, Yue Wang, Zhaomin HouAbstract:By use of the organolanthanide catalysts Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) and (C5Me5)2LaCH(SiMe3)2, carbazole-substituted phenyl Enynes (Z)-CPEY and (E)-CPEY were synthesized, respectively, with excellent regio- and stereoselectivity through the catalytic dimerization of the corresponding terminal alkyne. These new pi-conjugated compounds, in particular, the (E)-Enyne isomer (E)-CPEY, act as an excellent single-emitting component for white organic light-emitting devices (WOLEDs), as a result of combination of the blue emission from an isolated molecule with the longer-wavelength emissions (green and orange-red) from excimers. The (E)-CPEY-based double-layer device emitted almost pure white light with CIE coordinates of (0.32, 0.33), maximum brightness of 1395 cd m-2, and maximum current efficiency of 2.07 cd A-1. This is perhaps the purest white emission ever reported for a single-emitting-component WOLED. The quality of the white emission remained almost unchanged under varying driving voltages, demonstrating an advantageous potential of single-emitting-component WOLEDs.