藤田 守文

An oxetane intermediate during a direct aldol reaction was trapped with an internal aryl group to yield trans-tetraline products. The contribution of the oxetane intermediate was confirmed by 18O-isotope labeling experiments.

<p>The substitutions at the 2′- and/or 6′-positions of the quinoline ring of cinchonidine reduce both the intrinsic enantioselectivity and adsorption strength for the enantioselective hydrogenation of α-phenylcinnamic acid over Pd/C.</p>

© 2020 The Chemical Society of Japan. Enantioselective hydrogenations of α,β-unsaturated carboxylic acids over cinchona alkaloid-modified Pd metal heterogeneous catalysts have received considerable attention because of scientific importance in molecular recognition catalysis as well as feasibility of industrial applications. In the present study, comprehensive kinetic analysis of the hydrogenation was conducted to disclose the crucial kinetic parameters controlling enantiodifferentiation and reaction rate with the combinations of four kinds of modifier and three kinds of substrate. Despite simplicity of the kinetic model, the present novel kinetic formulation allows us to describe the enantioselectivity as a function of modifier concentration, to estimate intrinsic enantioselectivity at the modified sites, to estimate respective reaction rates at the modified and unmodified sites, and to establish a correlation between the magnitude of ligand acceleration and kinetic parameters. The enantioselectivity is successfully correlated to the reaction rate. The adsorption strength of the modifier on Pd is suggested to decrease in the order, cinchonidine > cinchonine > quinine > quinidine. The roles played by benzylammine and the observed decrease in the selectivity at a high modifier concentration are also discussed. The kinetic model and formulation can be applied to analyze the catalytic behaviors and performance of Pt counterparts.

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Abstract: The asymmetric hydrogenation of (E)-2,3-di(4-methoxyphenyl)propenoic acid was conducted over Pd/C chirally modified with cinchona alkaloids methyl-substituted at 2′-position of the quinoline ring. It is revealed that the adsorption strength of the modifiers and the intrinsic enantioselectivity at the modified sites are decreased by the methyl-substitution. The intrinsic enantioselectivity of the modifier is correlated to kinetic parameters. Graphic Abstract: [Figure not available: see fulltext.]

© 2019 The Chemical Society of Japan To ensure high enantiopurity of the product, enantio-differentiating hydrogenation of methyl acetoacetate over a (R,R)-tartaric acid-modified Raney nickel catalyst is normally performed under elevated H2-pressure (310 MPa). In this study, higher enantioselectivity than previously reported for methyl acetoacetate was achieved (92% ee) under low H2pressure of 0.42 MPa. Effects of reaction conditions on the enantioselectivity and hydrogenation rate were investigated using a low-pressure reaction system (<0.5 MPa of H2). It was found that impurities in the solvent greatly reduce the enantioselectivity of MAA. The low-pressure reaction system enabled a satisfactory kinetic approach. The reaction rate was well described by Langmuir-Hinshelwood formalism, verifying the previous assumption that the addition of adsorbed hydrogen to the substrate interacting with surface tartrate is a rate-determining step.

© 2019 The Chemical Society of Japan. In the enantioselecitve hydrogenation of (E)-2-methyl-2butenoic acid (1) over a cinchonidine-modified Pd/C catalyst, the addition of hydrogen preferentially proceeds from the Re-Si enantioface of the C=C double bond of 1 to yield (S)-2methylbutanoic acid ((S)-3). Double bond migration of 1 takes place under the reaction conditions and is followed by immediate hydrogenation to yield 3 in a poor enantiomeric purity. Deuterium labeling experiments at 0.1 MPa and 1.9 MPa of D2verified the previous assumption of competitive double bond migration. The combination of isotopic labeling experiments and chiral analysis revealed that the double bond migration of 1 proceeds with the same enantiofacial differentiation as the hydrogenation of 1. Thus, interaction of 1 with cinchonidine adsorbed on the Pd surface may control the configuration of the double bond migration and the hydrogenation.

© 2018 Fujita et al.; licensee Beilstein-Institut. License and terms: see end of document. A series of optically active hypervalent iodine(III) reagents prepared from the corresponding (R)-2-(2-iodophenoxy)propanoate derivative was employed for the asymmetric dioxytosylation of styrene and its derivatives. The electrophilic addition of the hypervalent iodine(III) compound toward styrene proceeded with high enantioface selectivity to give 1-aryl-1, 2-di(tosyloxy)ethane with an enantiomeric excess of 70-96% of the (S)-isomer.

© 2018 The Chemical Society of Japan. Chiral (R,R)-tartaric acid and NaBr-doubly modified Raney nickel (TA-MRNi) is a promising heterogeneous catalyst for enantioselective hydrogenation of prochiral β-keto esters. To obtain deeper insights into the factors ruling the enantioselectivity, enantiodifferentiating hydrogenation of substituted ketones was studied over TA-MRNi and NaBr-modified RNi by use of combined individual-competitive hydrogenation techniques. Relative equilibrium adsorption constants of the substrates were estimated to evaluate their relative interaction strength with adsorbed tartaric acid moiety. DFT calculations were also performed to estimate the interaction energy through hydrogen bonding, providing clear support to the kinetic analysis and surface model. It is concluded with the enantioselective hydrogenation of ketones over TA-MRNi that the enantioselectivity increases as the substrate-modifier interaction strength increases: Methyl acetoacetate (MAA) > acetylacetone (AA) ∼ 4-hydroxy-2-butanone (HB) > 2-octanone (2O).

© 2018 The Japan Institute of Heterocyclic Chemistry. The field of chiral hypervalent iodine chemistry has made significant progress in the past decade. This review focuses on enantioselective heterocycle formation induced by chiral hypervalent iodine reagents and catalysts. The enantioselective heterocyclizations are classified into the dearomatization of phenols (and naphthols), a-oxidation of carbonyl compounds, and oxidative vicinal difiuictionalization of alkenes. As a characteristic reaction of a hypervalent iodine oxidizing reagent, the 6-endo selective lactonization of orr/70-alkenylbenzoate is selected and compared with the 5-exo selectivity induced by other electrophilic reagents. The oxidative lactonization with 6-endo selectivity afforded a 4-oxyisocliroman-l-one framework, which has been found in a family of polyketide metabolites. The total syntheses of 4-oxyisochroman-l-one natural products were also summarized to assess the synthetic utility of hypervalent iodine compounds.

© 2017 Elsevier Ltd Recent progress in the area of hypervalent iodine-induced enantioselective oxidation is reviewed with emphasis from a mechanistic point of view. Chiral lactate and lactamide sidechains in hypervalent iodine reagents induce herical chirality around the iodine reaction site, which provides a chiral environment suitable for enantioselective transformations. The stereochemical outcomes of alkene oxidation are also compiled and used for systematically understanding the reaction mechanism of oxidative double bond difunctionalization.

© 2017 American Chemical Society. The oxidation of (5-acyloxypent-3-enyl)benzene with hypervalent iodine(III) afforded 2-oxy-1-(oxymethyl)tetrahydronaphthalene under metal-free conditions. The acyloxy group may nucleophilically participate in the oxidative cyclization. A lactate-based chiral hypervalent iodine afforded an enantioselective variant of oxyarylation with up to 89% ee.

© Georg Thieme Verlag Stuttgart. New York. Stereospecific inversion of configuration was observed in electrophilic iodo-substitution of 4-benzoyloxybut-1-enylboronate using bis(2,4,6-trimethylpyridine)iodine(I) salt, rationalized by participation of the internal benzoyloxy group.

© 2017 Japan Society for Bioscience, Biotechnology, and Agrochemistry. A unique electron-accepting analog of vitamin K1 found in photosystem I in several species of oxy-genic photosynthetic microorganisms was confirmed to be 5′-hydroxyphylloquinone (1) through stereo-uncontrolled synthesis. Furthermore, the stereochemistry of 1 obtained from Synechococcus sp. PCC 7942 was assigned to be 5′S using proline-catalyzed stereocontrolled reactions.

© 2017 Elsevier Ltd The photoisomerization, epoxidation, and cyclopropanation of chiral 2,4-pentanediol tethered cyclooctene were explored to examine the stereocontrollability of the tether. Photoisomerization of (2R,4R)-2,4-pentanediol-tethered cyclooctene achieved a de of 20% at a high Z/E ratio of 0.80 at 25 °C, while (2S,4R)-2,4-pentanediol-tethered cyclooctene yielded a lower de in spite of an even higher Z/E ratio. The epoxidation and cyclopropanation of 2,4-pentanediol tethered cyclooctene resulted in lower stereoselectivity compared with those of vinyl ether. We propose that the low de of the reactions of 2,4-pentanediol tethered cyclooctene is not attributable to the low stereocontrollability of 2,4-pentanediol tether, but due to the conformational multiplicity of the reactant site.

This article highlights my recent studies on development of optically active hypervalent iodine (III) reagents which have a chiral side chain derived from lactic acid. The lactate chiral side chain may nucleophilically interact with the iodine atom, and the interaction induces pseudo chirality of the iodine atom. Owing to the pseudo chirality, the iodine (III) reagent is able to highly distinguish the enantioface of an alkene substrate. Actually, the lactate-based hypervalent iodine (III) reagents have been used for various types of enantioselective oxidation leading to high ee. One of the stereoselective oxidations is applied to a crucial step for the asymmetric synthesis of 4-oxyisochroman -1-one natural products.

© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The enantioselective oxyarylation of (E)-6-aryl-1-silyloxylhex-3-ene was achieved using a lactate-based chiral hypervalent iodine(III) reagent in the presence of boron trifluoride diethyl etherate. The silyl ether promotes the oxidative cyclization, and enhances the enantioselectivity. In addition, the corresponding aminoarylation was achieved.

Stereoselective formation of substituted 1,3-dioxolanes was achieved through an assembly of three components: alkene, carboxylic acid and silyl enol ether. The reaction proceeded via stereospecific generation of a 1,3-dioxolan-2-yl cation intermediate during oxidation of alkene substrates with hypervalent iodine. The stereoselective trapping of the cation intermediate with silyl enol ether completed the formation of the dioxolane product.

© 2014 American Chemical Society. A sequence of oxidation reactions of alkenamides with hypervalent iodine is described. Oxidation of ortho-alkenylbenzamide substrates selectively gave isochroman-1-imine products. The products underwent further oxidation in the presence of a Pd salt catalyst leading to regioselective C-H acetoxylation at the 8-position. A series of oxidations was applied to the crucial steps of asymmetric synthesis of 4-hydroxymellein derivatives.

The first total syntheses of (12R)- and (12S)-12-hydroxymonocerins are described. The oxolane-fused isochroman-1-one framework is stereoselectively constructed via a double oxy-cyclization using a lactate-based chiral hypervalent iodine reagent. A catalytic variant of the double oxy-cyclization is also demonstrated using a chiral iodoarene as the precatalyst and m-CPBA as the co-oxidant. © The Royal Society of Chemistry.

Optically active (2S,4R)-2-hydroxy-4-pentyl enol ether was prepared for the first time and subjected to hydroxy-directed oxidations at the olefinic group. Treatment with m-chloroperbenzoic acid and tert-butyl hydroperoxide/vanadium acetylacetonate resulted in the same stereoface differentiation at the olefin, with diastereomeric excesses as high as 79% and 92%, respectively, whereas the stereochemistry of the products of subsequent nucleophilic additions of the hydroxy group was opposite. © 2013 Elsevier Ltd. All rights reserved.

In this study, the enantioselective oxylactonization of ortho-alk-1-enylbenzoates with chiral hypervalent iodine(III) reagents yielded 3-alkyl-4-hydroxyisochroman-1-ones with high enantiomeric purity (ca. 90 % ee). The enantioselective oxidation was also performed under catalytic conditions, in which a catalytic amount (10 mol-%) of a chiral iodoarene was oxidized to the hypervalent iodine species in situ using a stoichiometric co-oxidant, m-chloroperbenzoic acid (mCPBA). The catalytic oxidation mediated by chiral hypervalent iodine(III) species yielded enantiocontrolled syn products, while the direct oxidation of the substrate with mCPBA occurred as background oxidation to give racemic anti products. Under optimized conditions, the catalytic oxylactonization led to high levels of enantioselectivity (ca. 90 % ee) and improved syn/anti selectivities (ca. 80 % syn). The product distribution indicated that the lactate side-chain on the chiral iodoarene precatalyst plays an important role in enhancing both the enantioselectivity and the catalytic efficiency in the oxylactonization. Organocatalytic oxidation mediated by chiral hypervalent iodine derivatives provides a concise route to optically active 4-hydroxyisochroman-1-ones. The lactate moiety of the iodoarene precatalyst plays an important role in enhancing both the enantioselectivity and the catalytic efficiency. This reaction should set the basis for synthetic routes to many 4-hydroxyisochoman-1-one natural products and their analogs. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stereoselective oxylactonization of ortho-alkenylbenzoate with chiral hypervalent iodine is applied to the asymmetric synthesis of 4-oxyisochroman-1-one polyketide metabolites including 4-hydroxymellein (1), a derivative of fusarentin 2, monocerin (3), and an epimer of monocerin epi-3. © 2012 American Chemical Society.

Optically active 1,3-dioxolan-2-yl cation intermediates were generated during enantioselective dioxyacetylation of alkene with chiral hypervalent iodine(III). Regioselective attack of a nucleophile toward the intermediate resulted in reversal of enantioselectivity of the dioxyacetylation.

It&#039;s the hype: The asymmetric synthesis of 3-alkyl-4-oxyisochroman-1-one is achieved by oxylactonization of ortho-alk-1-enylbenzoate with a series of optically active hypervalent iodine(III) reagents prepared from lactate or valine as a chiral source (see scheme). The oxylactonization is highly regio-, diastereo-, and enantioselective. © 2010 Wiley-VCH Verlag GmbH &amp; Co. KGaA. © 2010 Wiley-VCH Verlag GmbH &amp; Co. KGaA.

Reaction of but-3-enyl camphanate and its derivatives with iodosylbenzene yielded tetrahydrofuran-3-yl camphanate with high diastereomeric ratio via a 1,3-dioxan-2-yl cation intermediate. The reaction using (IS)-camphanate as a chiral auxiliary preferentially gave (S)-3-acyloxytetrahydrofuran and (2S,3S)-3-acyloxy-2-silyltetrahydrofuran. (C) 2009 Elsevier Ltd. All rights reserved.

Reactions of pent-4-en-2-yl carboxylates and their derivatives with iodosylbenzene gave 2,4-disubstituted and 2,3,5-trisubstituted tetrahydrofurans with high diastereomeric ratio. The tetrahydrofuranylation may proceed via a 1,3-dioxan-2-yl cation intermediate generated by the participation of the internal acyloxy group in electrophilic attack of hypervalent iodine(111) toward acyloxyalkenes. Steric regulation owing to the cyclic structure of the cation accounts for the high stereo selectivity of the tetrahydrofuranylation. (c) 2008 Elsevier Ltd. All rights reserved.

Optically active methyl 2-[2-(diacetoxyiodo)phenoxy]propanoate and its derivative were prepared and used for oxygenation of but-3-enyl carboxylates leading to tetrahydrofuran-3-yl carboxylates as an enantiomerically enriched form. (c) 2007 Elsevier Ltd. All rights reserved.

Solvolyses of monomethoxy-and dimethoxyphenyl(phenyl)iodonium (ArI(+)Ph) tetrafluoroborates were carried out in methanol and 2,2,2-trifluoroethanol (TFE) at 130 degrees C. The solvolysis products include alkoxide substitution products (ArOR and PhOR) as well as iodoarenes (PhI and ArI). The ratios of ArOR/PhOR range from 8/2 to 4/6. The results are argued against formation of aryl cation. Copyright (c) 2007 John Wiley & Sons, Ltd.

General reactivities of vinyl iodonium salts are summarized, and reactions of cyclohexenyl, 1-alkenyl, styryl, and 2,2-disubstituted vinyl iodonium salts are discussed in relation to possible formation of vinyl cation intermediates. Primary vinyl cation cannot be generated thermally but rearrangement via neighboring group participation often occurs. Photosolvolysis to give primary vinyl cation is also discussed.

Reaction of 4-acyloxybut-1-enylsilanes with iodosylbenzene in the presence of BF3 center dot OEt2 gave 4-acyloxy-2-oxobutylsilane and 3-acyloxytetrahydrofuran-2-ylsilane via a 1,3-dioxan-2-yl cation intermediate, which is generated by participation of the acyloxy group during the electrophilic addition of iodine(III) to the substrate.

Ring opening reaction of alkylidenecyclopropanone acetals readily proceeds in the presence of Lewis or Bronsted acids to produce 1-alkylidene-2-oxyallyl cation, which is provided for the reaction with nucleophiles such as chloride, alcohols, siloxyalkenes, and furans. The reaction of this cation with the carbon nucleophiles gives products of [4 + 3] and [3 + 2] cycloaddition as well as those of nucleophilic addition. The modes of addition reactions are controlled by the oxy group of the cation and by the reaction conditions including solvent.