Carbohydrate‐Templated Asymmetric Diels–Alder Reactions of Masked <i>ortho</i>‐Benzoquinones for the Synthesis of Chiral Bicyclo[2.2.2]oct‐5‐en‐2‐ones

Luo, Shun‐Yuan; Jang, Yeong‐Jiunn; Liu, Jing-Yuan; Chu, Chong‐Sun; Liao, Chun‐Chen; Hung, Shang‐Cheng

doi:10.1002/ange.200802693

Angewandte Chemie

2008

DOI: 10.1002/ange.200802693

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Carbohydrate‐Templated Asymmetric Diels–Alder Reactions of Masked ortho‐Benzoquinones for the Synthesis of Chiral Bicyclo[2.2.2]oct‐5‐en‐2‐ones

Shun‐Yuan Luo

Yeong‐Jiunn Jang

Jing-Yuan Liu

et al.

Abstract: A sweet addition: Asymmetric [4+2] cycloaddition of masked ortho‐benzoquinones with various alkenols by using sugars as chiral auxiliaries (see scheme; Bn: benzyl) affords the optically pure bicyclo[2.2.2]oct‐5‐en‐2‐ones with excellent diastereoselectivity and in good yields.

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Cited by 11 publications

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“…We have published intriguing results of highly diastereoselective and asymmetric Diels−Alder reactions of MOBs with homochiral furans, which lead to highly functionalized tricyclic ring systems with four stereogenic centers . We have also developed carbohydrate-templated asymmetric Diels−Alder reactions of MOBs for the synthesis of optically active bicyclo[2.2.2]oct-5-en-2-ones . On the basis of this knowledge, our efforts turned toward the development of reactions of MOBs with homochiral nitroso compounds for the syntheses of valuable optically active intermediates for a wide variety of biologically important molecules.…”

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confidence: 99%

Syntheses of Optically Pure Conduramines via the Strategy of Hetero Diels−Alder Reaction of Masked o-Benzoquinones with Homochiral Nitroso Dienophiles

Yang

Devendar

et al. 2010

Org. Lett.

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confidence: 99%

Syntheses of Optically Pure Conduramines via the Strategy of Hetero Diels−Alder Reaction of Masked o-Benzoquinones with Homochiral Nitroso Dienophiles

Yang

Devendar

et al. 2010

Org. Lett.

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Recent Advances in the Chemistry of Masked Ortho‐Benzoquinones and Their Applications in Organic Synthesis

et al. 2017

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Masked ortho‐benzoquinones are important intermediates in organic synthesis that exhibit a rich and fascinating chemistry. Their functionally enriched structural skeleton makes them important scaffolds in organic synthesis. They undergo a variety of interesting reactions and have found wide applications, especially in the total synthesis of many natural products. The functionalities such as alkene, diene, carbonyl, enone, dienone and ketal inherent in their structure can interfere individually or collectively in chemical transformations, making their chemistry interesting as well as challenging. Here, the work on masked ortho‐benzoquinones is reviewed in terms of their reactions such as intermolecular and intramolecular Diels–Alder reactions, Michael additions, [3+2] cycloadditions, and Baylis–Hillman reactions; these reactions lead to the formation of highly functionalised heterocyclic and carbocyclic compounds that are otherwise difficult to access. This Focus Review summarises the developments in the chemistry of masked ortho‐benzoquinones and covers the literature from 2005 to 2016.

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Hydrogen Bonding and Alcohol Effects in Asymmetric Hypervalent Iodine Catalysis: Enantioselective Oxidative Dearomatization of Phenols

2013

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The enantioselective oxidative dearomatization of phenols and their analogues is a key reaction for the synthesis of several natural products. [1] Conventionally, enantioselective transition-metal catalysis has been used for these transformations. [1c-e] Recently, some research groups [2] have reported catalytic enantioselective oxidative dearomatization reactions using chiral hypervalent iodine compounds. [3] However, the catalytic activities and enantioselectivities are moderate, and the substrate scope of the oxidation reactions is limited to 1-naphthol derivatives. Herein, we describe the rationally designed chiral iodoarene 1, which is derived from chiral 2-aminoalcohol, as a chiral precatalyst for the first enantioselective catalytic oxidative dearomatization of phenol derivatives 3 to give the desired cyclohexadienone spirolactones 4 and the subsequent Diels-Alder adducts [4] 5 with high to excellent enantioselectivities (87-99 % ee, Scheme 1). Active iodine(III) species 2 would be generated in situ from C 2 -symmetric and conformationally flexible chiral iodoarene 1 and meta-chloroperoxybenzoic acid (m-CPBA). We envisioned that a suitable chiral environment might be constructed around the iodine(III) center via intramolecular hydrogen bonding interactions between the acidic amido protons and the iodine(III) ligands (L).A preliminary examination of 1 (10 mol %) in the oxidative dearomatization of 2,4-di-tert-butylphenol derivative 3 a with 1.2 equivalents of m-CPBA in chloroform gave cyclohexadienone 4 a in 72 % yield with 91 % ee (Table 1, entry 1). However, the chemical yield and enantioselectivity of 4 a were significantly reduced when the reaction was performed in distilled chloroform (entry 2). The commercial chloroform that we used (Nacalai Tesque Inc., Japan) contained a small amount (ca. 1 wt %) of ethanol as a stabilizer. Thus, we serendipitously found that both the chemical yield and enantioselectivity of 4 a could be improved to the same level as in entry 1 by the addition of 10 equivalents of ethanol in distilled chloroform (entry 3). Next, alcohol additives and solvents were investigated in detail, [5] and the best result was obtained using 25 equivalents of methanol as an additive and dichloromethane as a solvent Scheme 1. Chiral organoiodine(III)-catalyzed enantioselective oxidative dearomatization of phenols and subsequent Diels-Alder reactions. m-CPBA = meta-chloroperoxybenzoic acid, L = ligand, Mes = mesityl. Table 1: Oxidative dearomatization of 3 a. Entry Precat. Solvent Additive (equiv) Yield [%] ee [%]

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Carbohydrate‐Templated Asymmetric Diels–Alder Reactions of Masked ortho‐Benzoquinones for the Synthesis of Chiral Bicyclo[2.2.2]oct‐5‐en‐2‐ones

Abstract: A sweet addition: Asymmetric [4+2] cycloaddition of masked ortho‐benzoquinones with various alkenols by using sugars as chiral auxiliaries (see scheme; Bn: benzyl) affords the optically pure bicyclo[2.2.2]oct‐5‐en‐2‐ones with excellent diastereoselectivity and in good yields.

Cited by 11 publications

References 34 publications

Syntheses of Optically Pure Conduramines via the Strategy of Hetero Diels−Alder Reaction of Masked o-Benzoquinones with Homochiral Nitroso Dienophiles

Syntheses of Optically Pure Conduramines via the Strategy of Hetero Diels−Alder Reaction of Masked o-Benzoquinones with Homochiral Nitroso Dienophiles

Recent Advances in the Chemistry of Masked Ortho‐Benzoquinones and Their Applications in Organic Synthesis

Hydrogen Bonding and Alcohol Effects in Asymmetric Hypervalent Iodine Catalysis: Enantioselective Oxidative Dearomatization of Phenols

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