Cobalt‐katalysierte [4+2+2]‐Cycloaddition zur Synthese von 1,3,6‐Cyclooctatrienen

Hilt, Gerhard; Janikowski, Judith

doi:10.1002/ange.200800127

Cited by 15 publications

(3 citation statements)

References 66 publications

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“…Interestingly, the “ para ” product was obtained with high regioselectivity when the ligand was 1,2-bis(diphenylphosphino)ethane (dppe), while the “ meta ” product was selectively formed with the imine ligand ( E )-2,4,6-trimethyl- N -(pyridine-2-ylmethylene)aniline (Scheme ) . Besides this, the catalyst obtained from CoBr 2 (dppe) by reduction with Zn/ZnI 2 was shown to efficiently catalyze also other transformations, including 1,4-hydrovinylations, − [2 + 2 + 2] cycloadditions, , Alder-en reactions, − [4 + 2 + 2] cycloadditions, [2 + 2] cycloadditions, homo-Diels–Alder reactions, , isomerizations of 1,3-dienes, Glaser couplings, and benzannulations of conjugated enynes …”

Section: Introductionmentioning

confidence: 99%

Cobalt Catalysis in the Gas Phase: Experimental Characterization of Cobalt(I) Complexes as Intermediates in Regioselective Diels–Alder Reactions

et al. 2013

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In situ-formed cobalt(I) complexes are proposed to act as efficient catalysts in regioselective Diels-Alder reactions of unactivated substrates such as 1,3-dienes and alkynes. We report the first experimental evidence for the in situ reduction of CoBr2(dppe) [dppe = 1,2-bis(diphenylphosphino)ethane] by Zn/ZnI2 to [Co(I)(dppe)](+) by means of electrospray MS(n) experiments. Additionally, the reactivities of Co(II) and Co(I) dppe complexes toward the Diels-Alder substrates isoprene and phenylacetylene were probed in gas-phase ion/molecule reactions (IMRs). Isoprene and phenylacetylene were introduced into the mass spectrometer via the buffer gas flow of a linear ion trap. The IMR experiments revealed a significantly higher substrate affinity of [Co(I)(dppe)](+) compared with [Co(II)Br(dppe)](+). Furthermore, the central intermediate of the solution-phase cobalt-catalyzed Diels-Alder reaction, [Co(I)(dppe)(isoprene)(phenylacetylene)](+), could be generated via IMR and examined in the gas phase. Collision activation of this complex ion delivered evidence for the gas-phase reaction of isoprene with phenylacetylene in the coordination sphere of the cobalt ion. The experimental findings are consistent with the results of quantum-chemical calculations on all of the observed Co(I) dppe complex ions. The results constitute strong analytical evidence for the formation and importance of different cobalt(I) species in regioselective Diels-Alder reactions of unactivated substrates and identify [Co(I)(dppe)](+) as the active Diels-Alder catalyst.

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Section: Introductionmentioning

confidence: 99%

Cobalt Catalysis in the Gas Phase: Experimental Characterization of Cobalt(I) Complexes as Intermediates in Regioselective Diels–Alder Reactions

et al. 2013

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“…In contrast to the nickel‐catalyzed cyclotetramerization of alkynes (see Scheme ), cobalt‐catalyzed reactions of alkynes mainly lead to [2+2+2] cyclotrimerizations to form benzene derivatives. In 2008, Hilt31 et.al successfully coupled two alkynes with 1,3‐dienes to generate eight‐membered ring systems in an unprecedented three‐component [4+2+2] fashion (Scheme ). In this reaction, they utilized a cobalt catalyst in the presence of Zn, Fe, and ZnI 2 .…”

Section: [4+2+2] Cycloadditionsmentioning

confidence: 99%

Transition‐Metal‐Catalyzed Cycloadditions for the Synthesis of Eight‐Membered Carbocycles

Wang

2010

Chemistry An Asian Journal

170

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Eight-membered carbocycles are found in a wide variety of natural products that exhibit a broad range of biological and medicinal activities (cf. the most potent anticancer drug, taxol). However, the synthesis of eight-membered carbocycles is quite challenging as traditional approaches are met with entropic and enthalpic penalties in the ring-forming transition states. These negative effects can be totally or partially avoided with the implementation of transition-metal-catalyzed/mediated cycloadditions. In this Focus Review, examples of elegant and efficient metal-catalyzed and some metal-mediated cycloadditions (including Ni- catalyzed [4+4] and Rh-catalyzed [4+2+2] and [5+2+1] reactions) are presented to illustrate this. Application of these cycloaddition reactions in total synthesis is also presented to show the significance of these reactions in addressing challenges in natural product synthesis.

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“…[12,13] Diels-Alder, [14] homo-DielsAlder reactions, [15] and Alder-ene reactions, [16] [6 + 2], [17] reductive [3 + 2], [18] and [4 + 2 + 2] cycloadditions, [19] cyclizations of o-iodobenzoates with aldehydes, [20] aryl-sulfur bond formations, [21] Reformatsky reactions, [22] cross-couplings and conjugate additions [23] were also performed under these conditions. Therefore, common catalysts of type CpCoL 2 could be replaced by catalytic systems much easier to handle (and sometimes more efficient [11a] ) to generate benzenes or pyridines by [2 + 2 + 2] approaches.…”

Section: Introductionmentioning

confidence: 99%

A Straightforward Procedure for the [2+2+2] Cycloaddition of Enediynes

et al. 2009

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Enediynes undergo intramolecular [2 + 2 + 2] cycloaddition in the presence of cobalt(II) iodide (CoI 2 ), manganese and an N-heterocyclic carbene (IPr) generated in situ from the corresponding imidazolium salt and butyllithium (BuLi). Polycyclic cyclohexadienes are obtained selectively. This new method represents an interesting alternative to those employing air-sensitive cyclopentadi-Moreover, the N-heterocyclic carbene can be used catalytically, which is a significant improvement compared to the corresponding phosphine-based system which requires an excess of ligand.

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Cobalt‐katalysierte [4+2+2]‐Cycloaddition zur Synthese von 1,3,6‐Cyclooctatrienen

Cited by 15 publications

References 66 publications

Cobalt Catalysis in the Gas Phase: Experimental Characterization of Cobalt(I) Complexes as Intermediates in Regioselective Diels–Alder Reactions

Cobalt Catalysis in the Gas Phase: Experimental Characterization of Cobalt(I) Complexes as Intermediates in Regioselective Diels–Alder Reactions

Transition‐Metal‐Catalyzed Cycloadditions for the Synthesis of Eight‐Membered Carbocycles

A Straightforward Procedure for the [2+2+2] Cycloaddition of Enediynes

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