Acceleration effect of allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope and application to the synthesis of isofagomine

Imahori, Tatsushi; Ojima, Hidetomo; Tateyama, Hiroki; Mihara, Yukiko; Takahata, Hiroki

doi:10.1016/j.tetlet.2007.11.098

Cited by 36 publications

(10 citation statements)

References 44 publications

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“…Imahori et al have recently discovered that allylic hydroxy groups significantly enhance the rate of ring closing enyne metathesis reactions [ 53 – 54 ]. In these cases, addition of an ethylene atmosphere [ 55 ] which is normally considered to be mandatory for good results, is not required.…”

Section: Resultsmentioning

confidence: 99%

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

Krehl¹,

Geißler²,

Hauke³

et al. 2010

Beilstein J. Org. Chem.

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SummaryThe catalytic performance of NHC-ligated Ru-indenylidene or benzylidene complexes bearing a tricyclohexylphosphine or a pyridine ligand in ring closing metathesis (RCM), cross metathesis, and ring closing enyne metathesis (RCEYM) reactions is compared. While the PCy3 complexes perform significantly better in RCM and RCEYM reactions than the pyridine complex, all catalysts show similar activity in cross metathesis reactions.

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Section: Resultsmentioning

confidence: 99%

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

Krehl¹,

Geißler²,

Hauke³

et al. 2010

Beilstein J. Org. Chem.

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“…It is noteworthy that the four-step sequence from alcohol 4 23 to the corresponding cyano derivative 10 may be performed as a “one-pot” reaction without the need for isolation of the intermediate products. This process involves transient protection of 4 as a TMS ether with TMSCN under neutral conditions, which enables the selective deprotonation of the terminal acetylene with n -BuLi and subsequent cyanylation with PhOCN.…”

Section: Resultsmentioning

confidence: 99%

“…Alkyne 4 23 (2.88 g, 23.2 mmol) was dried over molecular sieves in DCM and transferred to a round bottom flask containing DCM (100 mL) at 0°C. Dry triethylamine (3.92 mL, 28.1 mmol) and a catalytic quantity of DMAP were then added followed by TBSCl (3.89 g, 25.8 mmol).…”

Section: Methodsmentioning

confidence: 99%

Facile access to cyclooctanoid ring systems via microwave-assisted tandem 6-exo dig cyclization–rearrangement sequence

Feldman

Ovaska

2014

Tetrahedron

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Appropriately substituted 5-alkyn-1-ol systems bearing a nitrile moiety at the triple bond serve as versatile precursors to a variety of cyclooctenone derivatives via a “one-pot” base-catalyzed oxyanionic 6-exo dig cyclization/Claisen rearrangement sequence under microwave irradiation. It was found that the initially formed cyclic intermediate consists of a mixture of endo and exocyclic isomers, which appear to be in equilibrium under the reaction conditions. However, the only observed products from these reactions are α-cyano substituted cyclooctenones, derived from the exocyclic dihydrofuran intermediates.

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“…This aspect is reinforced by the work of Imahori,18 who discovered that enyne substrates containing an allylic hydoxyl group undergo RCM with such efficiency that “Mori’s conditions” are not required. Kinetic studies18b supported an “ene‐then‐yne” mechanism in which the hydroxyl group accelerates product release from vinylalkylidene intermediate 5 , a process exploited in a synthesis of isofagomine 18a. We thus tested a range of simple allylic additives, including allyl alcohol, allyl benzyl ether, allyl cyanide, allyl dimethylmalonate, N ‐tosyl allylamine, allyl chloride and allyl bromide, at 50 mol % loading with enyne 1 a .…”

Section: Methodsmentioning

confidence: 98%

A Simple and Effective Co‐Catalyst for Ring‐Closing Enyne Metathesis Using Grubbs I type Catalysts: A Practical Alternative to “Mori’s Conditions”

Lloyd‐Jones

Robinson

Lefort

et al. 2010

Chemistry A European J

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In 1998 Mori reported [1] that ethylene improved turnover in the ring-closing metathesis (RCM) of enynes (1!2), [2] employing Grubbs generation I catalyst (3 a); for example, low yields of 2 a-c under 1 atm argon, became near-quantitative (99 %) under 1 atm. ethylene.[1] Subsequent kinetic analysis [3] revealed that ethylene not only increases the turnover frequency, but also reduces the impact of catalyst deactivation processes. The beneficial effect of ethylene is observed with many enyne substrates, particularly those with terminal alkyne moieties, and unsurprisingly, "Moris conditions" have been widely adopted (Scheme 1). [4] Two basic mechanisms have been proposed for the RCM of enynes involving intermolecular [5] metal-alkylidene propagation. These mechanisms are often referred to as the "yne-then-ene" and "ene-then-yne" pathways.[2] Evidence for both pathways has been presented, and phosphine catalysts, for example, 3 a, [6] appear to favour the "ene-then-yne" pathway (cycle A, Scheme 2). [7] For RCM involving phosphine catalysts, for example, 3 a, and terminal enynes, computational investigations [7,8] and isotopic labelling experiments [3] support earlier proposals [5b, 9] that ethylene acts as an alkene surrogate for the enyne (1) in the release of product (2) through alkene-alkylidene exchange with intermediate 5.[10] A second alkene-alkylidene exchange of 6 (R = H) with 1, to generate 4, connects the secondary cycle B with primary cycle A, [11] liberating the ethylene (R = H), which thus acts as a co-catalyst.During our earlier study of "Moris conditions" [3] we noted that co-reaction of the about threefold-faster-reacting substrate 1 c with 1 a resulted in a small but noticeable decrease in the rate of RCM of 1 a. This suggested to us that an appropriately "tuned" alk-1-ene might be able to act as an efficient co-catalyst, in a manner analogous to ethylene. Herein we report on a kinetic and isotopic labelling investigation into this concept, and the development of a simple alkene co-catalyst that provides practical advantage to "Moris conditions" for the RCM of terminal enynes using Grubbs I catalyst (3 a). Scheme 2. The "ene-then-yne" cycle (A) for RCM of enynes 1!2 and secondary cycle B to account for acceleration under "Moris conditions" in which R = H.

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Acceleration effect of allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope and application to the synthesis of isofagomine

Cited by 36 publications

References 44 publications

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

Facile access to cyclooctanoid ring systems via microwave-assisted tandem 6-exo dig cyclization–rearrangement sequence

A Simple and Effective Co‐Catalyst for Ring‐Closing Enyne Metathesis Using Grubbs I type Catalysts: A Practical Alternative to “Mori’s Conditions”

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Acceleration effect of allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope and application to the synthesis of isofagomine

Cited by 36 publications

References 44 publications

The catalytic performance of Ru–NHC alkylidene complexes: PCy3 versus pyridine as the dissociating ligand

The catalytic performance of Ru–NHC alkylidene complexes: PCy3 versus pyridine as the dissociating ligand

Facile access to cyclooctanoid ring systems via microwave-assisted tandem 6-exo dig cyclization–rearrangement sequence

A Simple and Effective Co‐Catalyst for Ring‐Closing Enyne Metathesis Using Grubbs I type Catalysts: A Practical Alternative to “Mori’s Conditions”

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The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand