Organoaluminum-promoted Claisen rearrangement of allyl vinyl ethers

Nonoshita, Katsumasa; Banno, Hiroshi; Maruoka, Keiji; Yamamoto, Hisashi

doi:10.1021/ja00157a049

Cited by 142 publications

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“…This result suggests that, in fact, both reaction pathways may be involved; however, the direct prenyl migration is apparently favored. Yamamoto and coworkers have proposed a transition state for this Lewis acid mediated rearrangement process 8b. As shown in Figure 2, the experimental results imply that the initial coordination of bulky aluminum catalyst (MABR) to prenyl ether 12 generates the sterically more favored complex A rather than the alternate complex B .…”

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confidence: 98%

“…We therefore decided to investigate a Lewis acid-catalyzed rearrangement of 5 . Upon screening a number of different catalysts, we were pleased to find that the bulky Lewis acid MABR ( 10 ), developed by Yamamoto and coworkers,8 showed the most promising results. As shown, treatment of illicinole 5 with MABR at −78 °C for 2 hours cleanly afforded illicinone 2 in 70 % yield.…”

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confidence: 99%

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Biomimetic total synthesis of tricycloillicinone and mechanistic studies toward the rearrangement of prenyl phenyl ethers

Lei¹,

Dai²,

Hua³

2008

Tetrahedron Letters

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The paper describes a short and biomimetic synthesis of tricycloillicinone, which was found to enhance the action of choline acetyltransferase (ChAT). The synthetic route has two critical reactions: bulky, oxygenophilic methylaluminum bis(4-bromo-2,6-di-tert-butylphenoxide) (MABR) promoted rearrangement of prenyl phenyl ether and photochemical cyclization. Furthermore, experiments were designed to explore the process of MABR promoted rearrangement. It was found that stereochemistry of deuterium labeled prenyl group was only partially scrambled, which suggests that there may be two possible reaction pathways involved in this process. It also suggests that the direct migration of prenyl group to para-position under these conditions is slightly favored over the Claisen-Cope process. The highly efficient synthetic route also provides important new opportunities to explore the biological behavior of tricycloillicinone.Tricycloillicinone (1, Scheme 1) is a member of an intriguing class of small molecule natural products that have been demonstrated to possess neurotrophic activity. Isolated from Illicium tashiroi by Fukuyama and coworkers in 1995, 1 tricycloillicinone was found to enhance the activity of choline acetyltransferase (ChAT), an enzyme required for the biosynthesis of the important neurotransmitter, acetylcholine. 2 Deficiencies in acetylcholine levels have been shown to be associated with the progression of neurodegenerative disorders, such as Alzheimer's disease. 3 It is therefore conceivable that a ChAT inducer, such as tricycloillicinone, could serve as a valuable lead compound in the development of novel therapeutic agents for the treatment of neurodegenerative diseases. 4 In 1998, our laboratory disclosed the first total synthesis of 1. 5 More recently, Terashima and coworkers reported the enantioselective total synthesis of tricycloillicinone. 6 Unfortunately, both of these synthetic routes are quite long, and the difficulties involved in gaining access to sufficient quantities of synthetic material have thus far limited our ability to perform all of the needed biological evaluations. We report herein the development of a rather more efficient, biomimetically inspired second generation total synthesis of tricycloillicinone. A key feature of this total synthesis involves rearrangement of a prenyl phenyl ether (see 5 → 2). In addition to exploiting this reaction for our total synthesis, we conducted experiments hoping to gain a © 2008 Elsevier Ltd. All rights reserved. *Corresponding author. Tel.: +1-212-639-5501; fax: +1-212-772-8691; e-mail: danishes@mskcc.org. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, an...

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confidence: 98%

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confidence: 99%

Biomimetic total synthesis of tricycloillicinone and mechanistic studies toward the rearrangement of prenyl phenyl ethers

Lei¹,

Dai²,

Hua³

2008

Tetrahedron Letters

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“…However, we were mindful that these substrates could also undergo a Lewis acid (LA) accelerated Claisen rearrangement, which if concerted, would form the [3,3] rearrangement product exclusively. [5] A number of workers have documented that the Lewis acid mediated Claisen rearrangement proceeds stepwise [6] and occasionally provides the [1,3] adduct with some selectivity. [7] To favor the [1,3] over the [3,3] product, we envisioned that a cyclic allylvinyl ether or 2,5-dihydrooxepin could provide access to densely functionalized cyclopentenes under ionizing conditions as the [3,3] rearrangement should be disfavored because of ring strain in the cyclopropane product [Eq.…”

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Stereoselective Lewis Acid Mediated [1,3] Ring Contraction of 2,5‐Dihydrooxepins as a Route to Polysubstituted Cyclopentenes

Nasveschuk

Rovis

2005

Angew Chem Int Ed

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“…However, we were mindful that these substrates could also undergo a Lewis acid (LA) accelerated Claisen rearrangement, which if concerted, would form the [3,3] rearrangement product exclusively 5. A number of workers have documented that the Lewis acid mediated Claisen rearrangement proceeds stepwise6 and occasionally provides the [1,3] adduct with some selectivity 7. To favor the [1,3] over the [3,3] product, we envisioned that a cyclic allylvinyl ether or 2,5‐dihydrooxepin could provide access to densely functionalized cyclopentenes under ionizing conditions as the [3,3] rearrangement should be disfavored because of ring strain in the cyclopropane product [Eq.…”

Section: Methodsmentioning

confidence: 99%

Stereoselective Lewis Acid Mediated [1,3] Ring Contraction of 2,5‐Dihydrooxepins as a Route to Polysubstituted Cyclopentenes

Nasveschuk

Rovis

2005

Angewandte Chemie

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Organoaluminum-promoted Claisen rearrangement of allyl vinyl ethers

Cited by 142 publications

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Biomimetic total synthesis of tricycloillicinone and mechanistic studies toward the rearrangement of prenyl phenyl ethers

Biomimetic total synthesis of tricycloillicinone and mechanistic studies toward the rearrangement of prenyl phenyl ethers

Stereoselective Lewis Acid Mediated [1,3] Ring Contraction of 2,5‐Dihydrooxepins as a Route to Polysubstituted Cyclopentenes

Stereoselective Lewis Acid Mediated [1,3] Ring Contraction of 2,5‐Dihydrooxepins as a Route to Polysubstituted Cyclopentenes

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