Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.tet.2022.132721

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/D1RA08706A

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>Synthesis of optically active 2-substituted azetidine-2-carbonitriles by LDA-promoted diastereoselective α-alkylation of borane <italic>N</italic>-((<italic>S</italic>)-1-arylethyl)azetidine-2-carbonitrile complexes was demonstrated.</p>

DOI： 10.1039/d1ra04585g

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.joc.0c01047

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tet.2020.131064

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/ejoc.201801448

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.tet.2018.12.058

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

DOI： 10.1039/c8ob01395k

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

DOI： 10.1039/c8ob01091a

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The base-induced Sommelet-Hauser rearrangement of N-alpha-branched benzylic azetidine-2-carboxylic acid ester-derived ammonium salts to obtain a-arylazetidine-2-carboxylic acid esters was investigated. The substrates, two diastereomeric salts (1S,2S,1'S)-and (1R,2R,1' S)-2, showed different reactivities. The rearrangement of (1S,2S,1'S)-2a proceeded with a perfect N-to-C chirality transfer to provide (R)-3a in 74% yield with 99% ee. However, the rearrangement of (1R,2R,1'S)-2a under the same conditions afforded (S)-3a in only 15% yield with a lower 66% ee, along with the competitive [1,2] Stevens rearrangement product 4a. Structural and mechanistic studies of this rearrangement were carried out to clarify the exact reason. Our results define the scope and limitations of the Sommelet-Hauser rearrangement and provide unique synthetic access to alpha-aryl amino acid derivatives.

DOI： 10.1039/c7ob01391d

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The base-induced Sommelet-Hauser (S-H) rearrangement of azetidine-2-carboxylic acid ester-derived ammonium salts into 2-aryl-substituted derivatives was demonstrated. The ring-strain of four-membered N-heterocycles enables efficient generation of the desired ylide intermediate and enhances the rate of the S-H rearrangement. The asymmetric version of the rearrangement was characterized by excellent levels of successive chirality transmissions. The regio- and stereo-controlled nucleophilic ring opening of the rearrangement products produced quaternary -aryl amino acid esters with excellent enantiopurities.

DOI： 10.1002/ejoc.201600611

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Authorship：Lead author,　Corresponding author   Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An overview of the utility of base-induced Stevens, Sommelet-Hauser, and related sigmatropic rearrangements of N-heterocyclic ammonium salts into various types of N-heterocycles reported after 1970 will be described. The synthetic transformations are classified as N-heterocyclic ring-substitution, ring-enlargement, and ring-contraction.

DOI： 10.3987/REV-16-837

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Oxidative ring-opening reactions of benzene-fused bicyclic cydopropyl silyl ethers, promoted by copper(II) tetrafluoroborate, were investigated. The regioselectivity of cyclopropane ring-opening as well as product distributions were found to be highly dependent on the nature of the solvent. In alcohols, dimeric substances arising from external bond cleavage are major products. Radical rearrangement products are also formed in solvents such as ether and ethyl acetate. On the contrary, nucleophile addition to carbocation intermediates, generated by internal bond cleavage, occurs mainly in reactions taking place in acetonitrile. It is proposed that the observed solvent effects that govern the reaction pathways followed are a consequence of varying solvation of copper intermediates, which governs their reactivity and redox properties. In addition, the influence of counteranions of the copper salts, organonitriles, cyclic dienes, and substrate structures on the pathways followed in these reactions was also examined.

DOI： 10.1021/acs.joc.5b02827

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The regioselective synthesis of secondary 1,3-dienamides 3 (1-N-acylamino-1,3-dienes) is successfully demonstrated by regiospecific base -promoted 1,4 -elimination of (Z)- or (E)-N,N-di-Boc-4-methoxy-2-buten-1 -ylamine 1 followed by mono-Boc elimination in situ. (C) 2015 Elsevier Ltd. All rights reserved,

DOI： 10.1016/j.tet.2015.11.065

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[5]Catenanes were synthesized by olefin metathesis dimerization. The reaction of pseudorotaxanes, which were derived from a [2]catenane and one equivalent of an ammonium salt bearing two terminal olefins in dichloromethane, with a catalytic amount of Grubbs catalyst afforded linear [5]catenanes in 12% yield. Intermolecular and intramolecular olefin metathesis reactions were controlled by the length of the alkyl chain of the ammonium salts.

DOI： 10.1039/c5cc07562a

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Diaza [1,4] Wittig-type rearrangement of N-allylic-N-Boc-hydrazines into gamma-amino-N-Boc-enamines was demonstrated. The scope and limitation, experimental mechanistic studies, and a proposed reaction mechanism were also described.

DOI： 10.1039/c6cc04626f

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEORG THIEME VERLAG KG  

The copper-catalyzed regiospecific and 1,2-regioselective cyclopropanation of (1Z)-1-amino- and (1Z)-1-oxy-1,3-butadienyl derivatives, which could be prepared by Z-stereoselective 1,4-elimination with a-aryl diazoesters was successfully demonstrated. This successful regiospecific protocol enabled the preparation of the corresponding 1-amino- and 1-oxy-2-vinylcyclopropane derivatives as almost single stereoisomers.

DOI： 10.1055/s-0034-1380426

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Photoinduced electron transfer (PET) reactions promoted by 2-aryl substituted 1,3-dimethylbenzimidazolines (Ar-DMBIH) were investigated. Excited states of Ar-DMBIH, formed by irradiation using light above 360 initiate PET reductions of various organic substrates, including transformations of epoxy ketones to aldols, free radical rearrangements such as the Dowd-Beckwith ring-expansion and 5-exo hexenyl cyclization, deprotection of N-sulfonyl-indols, and allylation of acyl formates. In these processes, Ar-DMBIH possessing 1-naphthyl, 2-naphthyl, 1-pyrenyl and 9-anthryl substituents formally act as two electron and one proton donors while the hydroxynaphthyl substituted derivative serves as a two electron and two proton donor. On the basis of the results of absorption spectroscopy studies, cyclic voltammetry and DFT calculation, a mechanistic sequence for these reduction reactions is proposed that involves initial photoexcitation of the aryl chromophore of the Ar-DMBIH followed by single electron transfer (SET) to the organic substrate to generate the radical cation of benzimidazoline and the radical anion of the substrate. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2015.06.071

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The Sommelet-Hauser rearrangement of N-benzylic ammonium ylides generated from ammonium salts is an interesting and useful transformation that enables one to convert a readily accessible C-N bond into a new C-C bond to an aromatic ring. The rearrangement was discovered by Sommelet in 1937, studied in detail by Hauser, and applied to organic synthesis by Sato until 1999. Further studies have not advanced because several competitive side reactions and structural limitations of the products severely limit the substrate scope and synthetic applications. In this Personal Account, a history of the research in problem solving and recent advances in the base-induced Sommelet-Hauser rearrangement are described. This synthetic method developed by my group provides efficient access to various types of -aryl--amino acid and -aryl--amino acid derivatives.

DOI： 10.1002/tcr.201500009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to beta-hydroxy ketones and alpha-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate ((BF3OEt2)-O-.) generates the cationic intermediates by regioselective epoxide ring opening and an acyl shift. Then, a treatment of these cations with 2-aryl-1,3-dimethylbenzimidazolines (DMBIH) results in formation of 1,2-disubstituted 3-hydroxy ketones. DMBIH serves as a hydride donor in the second step of this process. Finally, the beta-hydroxy ketones can be converted to 1,2-disubstituted 2-methylene ketones by treatment with methanesulfonic acid or a combination of methanesulfonyl chloride and triethylamine. Importantly, the sequential steps involved in formation of the alpha-methylene ketone products can be carried out in one pot.

DOI： 10.1021/jo5025249

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The base-promoted 1,4-elimination reaction of N-Boc-1-amino-4-methoxy-2-alkene 1 is shown to proceed with perfect stereoselectivity to afford the corresponding N-Boc-1-amino-1,3-diene 2 in good yields. The reaction is highly stereospecific. The substrate E-1 gave 1Z-2 by the 'Syn-Effect' and Z-1 gave 1E-2 via formation of a chelated intermediate. Our method is widely applicable to the preparation of various types of N-Boc-1-amino-1,3-dienes 2. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2014.12.039

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Copper(II)-acid catalyzed cyclopropanation of electron-rich alkenes, such as 1,3-dienamides, with cc-aryl diazoesters are described. The reaction could be performed without rare metal catalysts, excess substrate, or the need for the slow addition of the diazoesters. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2014.03.115

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A combination of 2-aryl substituted 1,3-dimethyl-benzimidazolines (DMBIHs) and tris(2,2'-bipyridine) ruthenium(II) chloride, Ru(bpy)(3)Cl-2 was used to promote photoinduced electron-transfer (PET) reactions of alpha-halomethyl-substituted benzocyclic 1-alkanones. This photo-reagent system stimulates free radical forming, cleavage of both carbon-bromine and carbon-chlorine bonds that are not activated by carbonyl groups. The resulting free radicals undergo 5-exo hexenyl cyclization as well as sequential cyclization and ring-expansion (Dowd-Beckwith) reactions to form radicals that abstract hydrogen atoms from the radical cation of DMBIH to yield the observed products. The results of a study of the effects of substituents located on the 2-aryl ring of DMBIH suggest that steric and hydrogen-bonding interactions influence the nature of the reaction pathways followed by the radical intermediates. PET reactions using an iridium complex and DMBIH were also investigated. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2014.02.078

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC SYNTHETIC ORGANIC CHEM JPN  

The Sommelet-Hauser rearrangement of N-benzylic ammonium ylides generated from tetraal-kylammonium salts is an interesting and useful transformation in organic synthesis that can provide easy access to ortho-substituted aromatic compounds. The base-induced rearrangement of an N-chiral-N-benzylic proline-derived ammonium salt or N-benzylic amino acid (-)-8-phenylmenthol ester-derived ammonium salts is shown to proceed in excellent yields with perfect levels of diastereoselectivity without any detectable amount of the [1,2] Stevens rearrangement product. A solution of potassium tert-butoxide in THF was shown to remarkably enhance the base-induced Sommelet-Hauser rearrangement of N-benzylic amino acid-derived ammonium salts. The reaction proceeds under mild conditions with minimal competition from the [1,2]-Stevens rearrangement. These methods provide efficient access to alpha-aryl-alpha-amino acid, alpha-aryl-beta-amino acid, and alpha-arylpipecolinic acid derivatives.

DOI： 10.5059/yukigoseikyokaishi.72.418

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The base-induced asymmetric [2,3] Stevens rearrangement of N-cinnamyl tetraalkylammonium ylides derived from L-alanine amides proceeds via a double axially chiral intermediate to afford the corresponding alpha-substituted alanine derivatives with high enantio-and diastereoselectivities.

DOI： 10.1039/c4cc02536a

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A photoreaction between benzoyl compounds, such as benzoylformate derivatives, and 2-(p-anisyl)-1,3-dimethylbenzimidazoline in the presence of allyl bromide was found to give various allylated alcohols. In the reaction of benzoylformates, cc-hydroxy ester enolates, for which the negative charge occurs on the carbonyl carbon of benzoyl (umpolung reactivity), are proposed to be generated as intermediates by electron-transfer from benzimidazolines to the photoexcited benzoylformates; these species react with allyl bromide to produce alpha-allyl-alpha-hydroxy esters. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2013.10.028

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BEILSTEIN-INSTITUT  

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives were investigated. The regioselectivities of these processes were found to be influenced by the structure of cyclopropanols as well as the counter anion of the copper(II) salts. A mechanism involving rearrangement reactions of radical intermediates and their competitive trapping by copper ions is proposed.

DOI： 10.3762/bjoc.9.156

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The syntheses of [2]- and [3]catenanes by olefin metathesis and oxidative acetylide coupling have been studied in detail. Pseudorotaxanes that were obtained by mixing crown ether and ammonium salts containing two terminal reactive end-groups were converted to [2]- and [3]catenane. Their yields were influenced not only by the chain length of the ammonium salts but also by the concentration of the crown ether and the ammonium salts. The strain energies of [2]catenane were responsible for the formation of [2]catenane.

DOI： 10.1021/jo400239h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The 1,4-elimination reaction of (Z)-N-Boc-2-(4-methoxy-2-alkenyloxy)amines with Bronsted acids catalyzed aza-Ferrier reaction of the 1,4-eliminated product, thus obtained, afforded various beta-amino-beta,gamma-unsaturated aldehydes. The scope and limitation of this sequential reaction are described. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2013.01.088

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A unique and simple preparative method for N-cyano-alpha-arylpipecolinic acid esters via base-induced Sommelet-Hauser rearrangement, the von Braun reaction, and intramolecular alpha-alkylation is reported. The removal of the N-cyano substituent was achieved by hydrogenation and hydride reduction.

DOI： 10.3987/COM-12-12619

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Aza-Prins cyclization reactions of N-tosyl-3-butenylamine with p-methoxybenzaldehyde, 1-naphthaldehyde and 2-naphthaldehyde take place efficiently using a combination 1-butyl-3-methylimidazolium of ferric chloride and hexafluorophosphate in benzotrifluoride (Felm-BTF procedure). The new methodology, leading to formation of target N-tosyl-4-chloro-2-substituted piperidines, is superior to the one using 1-butyl-3-methylimidazolium tetrachloroferrate. The Felm-BTF procedure was also applied to aza-Prins cyclization reactions of other aldehydes. Finally, the effects of imidazolium salts on aza-Prins cyclization reaction promoted by boranetrifluoride-diethyl ether complex, leading to formation of fluorinated piperidines, were explored.

DOI： 10.3987/COM-12-S(N)78

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The intermolecular aromatic substitution of N,N-dialkylanilines and alkoxybenzenes with diazoesters is shown to proceed in the presence of catalytic amounts of both copper(II) salt and acid (Lewis or Bronsted). This method is a mild and rare metal-free C-C bond formation reaction between aromatic (sp(2)) and aliphatic (sp(3)) carbons. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2012.07.070

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Selective amine de-alkylation enables the conversion of Sommelet-Hauser rearrangement products into 2-aryl-2-bromoacetic acid derivatives. These compounds are valuable synthetic intermediates in the synthesis of alpha-aryl-alpha-amino or alpha-aryl-beta-amino acid derivatives. The method presented herein is a formal de-N,N-dialkylation of Sommelet-Hauser rearrangement products. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2012.04.015

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A new protecting group, 1,2-dimethoxy-4,5-dimethylene, for acyclic amino acid derivatives could be introduced by N,N-dialkylation with 1,2-bis(bromomethyl)-4,5-dimethoxybenzene (1) and removed via amine de-alkylation with acyl chlorides. The method can be used with base-induced [2,3] and [1,2] Stevens rearrangement products. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2012.01.013

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Asymmetric alpha-2-tosylethenylation of (S)-2-(pyrrolidin-1-yl)propanoic acid esters was shown to produce good yields with high enantioselectivities. The reaction proceeds via the formation of a non-racemic ammonium enolate without an external source of chirality.

DOI： 10.1039/c1ob06074k

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Asymmetric alpha-2-tosylvinylation of N-substituted proline esters using ethynyl tolyl sulfone as an electrophile was shown to proceed in good yield with high enantioselectivities without the addition of any bases. The reaction proceeds via the formation of N-2-tosylvinyl ammonium ylides. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2011.02.040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The intermolecular aromatic substitution of N,N-disubstituted anilines with diazo esters is achieved under mild conditions in the presence of a catalytic amount of copper(II) triflate (up to 89% yield). The scope and limitations regarding substrates, diazo esters, and ligands in this reaction are described.

DOI： 10.1002/ejoc.201001083

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Aza-Prins cyclization reaction of N-tosyl-3-butenylamine with aliphatic and aromatic aldehydes was performed using a combination of FeCl3 and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) or 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl(4)) in benzotrifluoride (BTF). The desired N-tosyl-4-chloro-2-substituted piperidines were obtained from aliphatic aldehydes in comparable yields to those for the previously reported reactions in which FeCl3 was used in CH2Cl2. On the other hand, significant progress for the piperidine synthesis from aromatic aldehydes has been achieved, particularly when BmimFeCl(4) was used with FeCl3 in BTF. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2010.10.018

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A solution of potassium tert-butoxide in THF was shown to remarkably enhance the base-induced Sommelet-Hauser rearrangement of N-benzylic amino acid-derived ammonium ylides. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2010.09.125

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The resolution of N-chiral, amino acid-derived quaternary ammonium salts is demonstrated by using chiral BINOL as a complexing agent. Determination of the enantiopurities and absolute configurations of the resolved N-chiral tetraalkylammonium salts are described. The [1,2] Stevens rearrangement of N-chiral ammonium salts is shown to proceed with N-to-C chirality transmission to afford optically active 3-substituted morpholin-2-one derivatives. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2009.10.025

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The Stevens rearrangement of N-allylic alpha-aryl amino acid-derived ammonium salts and the Sommelet-Hauser rearrangement of N-benzylic alpha-alkyl amino acid-derived ammonium salts are shown to proceed with remarkably high levels of diastereoselectivity. The methods presented in this work provide new routes to optically active alpha-quaternary alpha-aryl amino acid derivatives.

DOI： 10.1039/b811162f

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The 1,4-elimination reaction of (Z)-N-Boc-2-(4-methoxy-2-alkenyloxy)pyrrolidines (1) is shown to proceed with high (1E, 3E)-stereoselectivity to afford N-Boc-2-(1,3-dienyloxy)pyrrolidines (2); the Bronsted acid catalyzed aza-Ferrier reaction of the N-Boc-2-(1,3-dienyloxy) pyrrolidines (2) provides alpha-(N-Boc-2- pyrrolidinyl) aldehydes (3) in excellent yields with high alpha-regioselectivities.

DOI： 10.1039/b806492j

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The 1,4-elimination reaction of 2-substituted-(2Z)-4-methoxy-O-alkenyl acetals with n-butyllithium is shown to afford the 2-substituted-(1Z,3E)-O-1,3-dienyl acetals in high stereoselectivities. The Ferrier reaction of the O-1,3-dienyl acetals thus obtained provides the corresponding alpha-quaternary-beta,gamma-unsaturated aldehydes in excellent yields with high alpha-regioselectivities. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2007.09.049

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The 1,4-elimination reaction of 1-amino-4-methoxy-(2Z) -alkenes is shown to proceed with high (1E,3E)-stereoselectivities to afford the corresponding 4-substituted-1-amino-1,3-dienes in good yield. The scope and stereochemical features of the synthetic method are described. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2007.06.140

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The optical resolution of nitrogen-centered chiral beta-hydroxy-tetraalkylammonium bromides is demonstrated by using chiral BINOL as a complexing agent. Determination of the enantiopurities and absolute configurations of the resolved N-chiral tetraalkylammonium salts are described. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2007.04.078

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.200703832

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The Ferrier reaction of O-1,3-dienyl acetals promoted by organoaluminum complexes such as methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) is shown to proceed with a high degree of regio- and stereoselectivity to afford the corresponding alpha-alkenyl-substituted beta-alkoxy aldehydes in good yields. The mechanistic origin of the high regiocontrolling ability of MAD is elucidated. This method, coupled with the easy availability of the requisite substrates, expands the synthetic scope of the Ferrier reaction.

DOI： 10.1021/ol062042j

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The 1,4-elimination reaction of 1-allyloxy-4-methoxy-(2Z)-alkenes with n-butyllithium is shown to proceed in a marked preference to the [2,3] Wittig rearrangement to afford the allylic (1Z,M)-dienyl ethers in high stereoselectivities. The synthetic utility of this method is demonstrated by the Claisen rearrangement of the dienyl ethers thus obtained. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2006.08.100

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The Stevens rearrangement of (S)-N-benzylic proline-derived ammonium salt with cesium hydroxide in 1,2-dichloroethane is shown to proceed with a high degree of the N-to-C chirality transmission to afford the alpha-substituted proline derivatives in high enantio-purities.

DOI： 10.1246/cl.2006.478

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEORG THIEME VERLAG KG  

Treatment of l-alkoxy-4-methoxy-(2Z)-alkenes or l-siloxy-4-methoxy-(2Z)-alkenes with n-butyllithium in diethyl ether is shown to afford the corresponding (1Z,3E)-dienyl, alkyl or silyl ethers, respectively, in high stereoselectivity via a facile 1,4-elimination. The scope and the regio- and stereochemical features of the synthetic method are described.

DOI： 10.1055/s-2006-939053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The asymmetric [2,3] Stevens rearrangement of epimeric mixtures of N-allylic ammonium salts derived from (5R)-5-phenyl-1,4-oxazin-2-one is shown to proceed with efficient kinetic resolution to afford the unnatural alpha-amino acid derivatives in high enantio-purities.

DOI： 10.3987/COM-05-S(K)39

DOI： 10.3987/com-05-s(k)39

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Highly enantioselective alkylation of protected glycine diphenylmethyl (Dpm) amide 1 and Weinreb amide 10 has been realized under phase-transfer conditions by the successful utilization of designer chiral quaternary ammonium salts of type 4 as catalyst. Particularly, remarkable reactivity of the chiral ammonium enolate derived from 1b and 4c allowed the reaction with less reactive simple secondary alkyl halides with high efficiency and enantioselectivity. An additional unique feature of this chiral ammonium enolate is its ability to recognize the chirality of beta-branched primary alkyl halides, which provides impressive levels of kinetic resolution and double stereodifferentiation during the alkylation, allowing for two alpha- and gamma-stereocenters to be controlled. Combined with the subsequent reduction using LiAlH4 in cyclopentyl methyl ether (CPME), this system offers a facile access to structurally diverse optically active vicinal diamines. Furthermore, the optically active a-amino acid Weinreb amide 11 can be efficiently converted to the corresponding amino ketone by a simple treatment with Grignard reagents. In addition, reduction and alkylation of the optically active alpha-amino ketone into both syn and anti alpha-amino alcohols with almost complete relative and absolute stereochemical control have been achieved. With (S,S)- and (R,R)-4 in hand, the present approach renders both enantionners of alpha-amino amides including Weinreb amides readily available with enormous structural variation and also establishes a general and practical route to vicinal diamines, a-amino ketones, and a-amino alcohols with the desired stereochemistry.

DOI： 10.1021/ja0459328

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Other Link： http://orcid.org/0000-0002-0309-9507

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/ja043898r

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Other Link： http://orcid.org/0000-0002-0309-9507

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Lewis acid catalyzed direct vinylogous Mannich-type reaction with a weak nucleophile dienol, generated in situ by ringopening and rearrangement of vinyloxiranes, could be demonstrated in excellent yields under mild conditions using benzylidene(4-methoxy-2-trifluoromethvl)aniline (MTMA) as an electrophile. The o-trifluoromethyl substituent can stabilize imines by a steric effect and activate by an electron-withdrawing effect. It proved to be an easily deprotectable protecting group for direct Mannich-type reactions. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2004.04.165

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

The asymmetric phase-transfer catalytic alkylation of peptides has been achieved by the use of designed C-2-symmetric chiral quaternary ammonium bromide 1 as catalyst. Excellent stereoselectivities were uniformly observed in the alkylation with a variety of alkyl halides and the efficiency of the transmission of stereochemical information was not affected by the side-chain structure of the preexisting amino acid residues. This method also enables an asymmetric construction of noncoded alpha,alpha-dialkyl-alpha-amino acid residues at the peptide terminal. Since this chirality can be efficiently transferred to the adjacent amino acid moiety, our approach provides a general procedure not only for the highly stereoselective terminal functionalization of peptides but also for the sequential asymmetric construction of unnatural oligopeptides, which should play a vital role in the peptide-based drug discovery process.

DOI： 10.1073/pnas.0307725101

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Other Link： http://orcid.org/0000-0002-0309-9507

Language：English   Publisher：AMER CHEMICAL SOC  

A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction. The structure of the bidentate Lewis acid 2 was unambiguously determined by single-crystal X-ray diffraction analysis of 2g possessing a bulky 3,5-di-tert-butylphenyl substituent, revealing the rigid dimeric assembly in the solid state. The double electrophilic activation of carbonyl substrate by 2a has been supported by low-temperature C-13 NMR analysis as well as theoretical study using the Gaussian 98 program. Moreover, unique stereoselectivity has been observed in the 2a-promoted Mukaiyama Michael addition, and highly chemoselective functionalization of carbonyl compounds in the presence of their acetal counterparts has been realized using 2a. Finally, the effectiveness of 2a for the activation of ether functionality has been demonstrated in the Claisen rearrangement of allyl vinyl ethers.

DOI： 10.1021/ja030552s

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Other Link： http://orcid.org/0000-0002-0309-9507

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The first synthetic application of 2-methyl-2-vinyloxirane as a masked dienolate has been successfully demonstrated in the direct vinylogous Mannich-type reaction with an alpha-imino ester as an electrophile. The Mannich adduct was a useful intermediate en route to cis-5-substituted pipecolinic acid ethyl ester under simple hydrogenation conditions.

DOI： 10.1021/ol036153j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.200352658

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Other Link： http://orcid.org/0000-0002-0309-9507

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.200390167

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Chiral bis(organoaluminum) Lewis acids have been newly designed and synthetic utility of their eminent activation ability of an ether functionality has been successfully demonstrated by the application to asymmetric Claisen rearrangement of allyl vinyl ethers. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4020(02)00981-X

DOI： 10.1016/s0040-4020(02)00981-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A remarkable template effect in the intramolecular radical cyclization process has been observed by the successful utilization of Lewis acid receptor, aluminum tris(2,6-diphenylphenoxide) (ATPH). The origin of this efficient template effect by ATPH would be ascribable to the well-defined reaction environment created in front of the aluminum coordination center; this enables appropriate proximity of initially generated carbon radical to unsaturated carbon-carbon bond in the transition state for smooth cyclization and hence completely suppresses the undesired intermolecular reduction pathway. Moreover, such conformational restriction provided by the unique cavity of ATPH alters the stereoselectivity of the cyclization. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4020(00)01007-3

DOI： 10.1016/s0040-4020(00)01007-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEORG THIEME VERLAG  

Significant rate enhancement was observed in the liquid-liquid phase-transfer catalytic epoxidations and alkylations under ultrasonic irradiation. Its advantage was also demonstrated in the asymmetric alkylation of tert-butyl glycinate-benzophenone Schiff base using C-2-symmetric chiral phase-transfer catalyst.

DOI： 10.1055/s-2000-7652

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

New type of fluoride ion catalyzed allylation agent (1a, 1b), allenylation agent (9, 10), and alkynylation agent (17) can be successfully utilized for various carbonyl substrates. The rate acceleration is ascribable to the shift of equilibrium to the chelate complexes with Bu4NF by the favorable chelation of bis(silyl) compounds toward the fluoride ion. The F-19 NMR spectrum (ethyl trifluoroacetate as external standard) of a mixture of 1a and Bu4NF in CDCl3 showed two peaks at delta -81.75 and -77.67 (integration ratio similar to 9:1). The large signal corresponds to the original peak of Bu4NF and the small one might be ascribed to the chelate complex [B] between la and Bu4NF. The fluoride ion mediated reaction of bis(crotyldimethylsilyl)methane (7) with benzaldehyde was examined and the only gamma-adduct 8 was obtained regioselectively. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4020(00)00458-0

DOI： 10.1016/s0040-4020(00)00458-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEORG THIEME VERLAG  

Convenient, efficient preparation of aromatic sec-amides from esters has been accomplished using dilithium amides which are easily prepared by treatment of aromatic amines with 2 equiv of BuLi in THF. This new method allows a facile formation of amide bond even with sterically hindered esters.

DOI： 10.1055/s-1999-2731

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Chemoselective functionalization of carbonyl compounds over acetals has been achieved by bidentate organoaluminum Lewis acid based on the selective double electrophilic activation of carbonyls. (C) 1997 Elsevier Science Ltd.

DOI： 10.1016/S0040-4039(97)01735-8

DOI： 10.1016/s0040-4039(97)01735-8

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