Showing papers by "Hisashi Yamamoto published in 2007"
TL;DR: New chiral bishydroxamic acids were synthesized and tested as chiral ligands in the vanadium-catalyzed asymmetric epoxidation of homoallylic alcohols to provide good yields and high enantioselectivities.
Abstract: New chiral bishydroxamic acids were synthesized and tested as chiral ligands in the vanadium-catalyzed asymmetric epoxidation of homoallylic alcohols to provide good yields and high enantioselectivities.
162 citations
TL;DR: Cationic oxazaborolidine 2 affords Diels−Alder adducts of ethyl acrylate and 2-substituted cyclopentadienes, derived from the corresponding mixture of regioisomers, as single isomers in excellent yields and enantioselectivities.
Abstract: Cationic oxazaborolidine 2 affords Diels−Alder adducts of ethyl acrylate and 2-substituted cyclopentadienes, derived from the corresponding mixture of regioisomers, as single isomers in excellent yields and enantioselectivities. Furthermore, Diels−Alder adducts of 1-substituted cyclopentadienes are obtained through a one-pot procedure whereby ethyl acrylate is initially employed to consume all 2-substituted cyclopentadiene. Subsequently, various 2,5-disubstituted benzoquinones are added to react with remaining 1-substituted cyclopentadiene. Remarkably, reaction occurs selectively at the double bond coordinated anti to catalyst 2 to provide adducts containing adjacent all-carbon quaternary stereocenters in high yields and excellent enantioselectivities.
99 citations
TL;DR: New chiral tethered bis(8-quinolinolato) (TBOx) aluminum(III) complexes effectively catalyze the highly enantioselective Mukaiyama−Michael reaction of silyl enol ethers, including tetrasubstituted enolates that give rise to enantioenriched α-carbonyl all-carbon-substituting quaternary stereocenters.
Abstract: New chiral tethered bis(8-quinolinolato) (TBOx) aluminum(III) complexes effectively catalyze the highly enantioselective Mukaiyama−Michael reaction of silyl enol ethers, including tetrasubstituted ...
69 citations
TL;DR: The development and preliminary results of the new designed C(2)-symmetric bis-hydroxamic acid ligands are described and it is demonstrated the versatile nature of BHA in the molybdenum catalyzed asymmetric oxidation of unfunctionalized olefins and sulfides.
56 citations
TL;DR: A number of new synthetic methods are reviewed in this article, most of which are based on aluminum, boron, tin, silver Lewis acids and/or Bronsted acid catalysts.
49 citations
TL;DR: In this paper, the TBOxCrIIICl/TBOxcrII system is used for catalytic asymmetric redox process. Because of the electron density, high turnover numbers are expected, hence allowing decrease in t...
Abstract: The TBOxCrIIICl/TBOxCrII system is ideal for catalytic asymmetric redox process. Because of the electron density of the TBOxH ligand high turnover numbers are expected, hence allowing decrease in t...
21 citations
TL;DR: In this article, a mini-review of the rapidly growing field of Bronsted acid catalysts is presented. But the authors do not discuss the use of any transition metal catalysts.
Abstract: This mini-review concerns the rapidly growing field of Bronsted acid catalysis. Bronsted acid catalysts are able to play an important role in green chemistry. Without the use of any transition metal catalysts, various organic transformations including asymmetric synthesis can be performed efficiently. This review summarizes our recent results in this field.
16 citations
TL;DR: New chiral bishydroxamic acids were synthesized and tested as chiral ligands in the vanadium-catalyzed asymmetric epoxidation of homoallylic alcohols to provide good yields and high enantioselectivities.
Abstract: New chiral bishydroxamic acids were synthesized and tested as chiral ligands in the vanadium-catalyzed asymmetric epoxidation of homoallylic alcohols to provide good yields and high enantioselectivities.
9 citations
TL;DR: In this article, the effect of a tris(trimethylsilyl) silicenium ion (TTMSS+) adjacent to a silicium ion could be determined.
Abstract: We recently developed a new use of the super silyl group in organic reactions, and showed that it has unique reactivity. One of the reactions using this reagent is diastereoselective Mukaiyama aldehyde cross-aldol reaction catalyzed by a highly active Bronsted acid. This reaction produced syn-1,3-diol derivatives with high yield and high stereoselectivity. Certain features and outcomes of the reaction were not clear, so we decided to investigate the reaction mechanism through a theoretical study. In this paper, structures of super silyl species were observed as the subject of study. First 1 and 2 were investigated so that the effect of a TMS group adjacent to a silicenium ion could be determined. Interestingly, it was found that the TMS group stabilized the silicenium ion. It is presumed that the stability of the tris(trimethylsilyl) silicenium ion (TTMSS+) is related to the unique reactivity of super silyl group in theses reactions. We also investigated equivalent structures of silyl enol ethers (SEE) and found an unusual structure of 5. This structure is a result of unusual interactions between the silyl portion and enol ether (EE) portion; 1) C=C and Si-Si bonds, 2) lone pair of oxygen and Si-Si bond.
5 citations
TL;DR: In this paper, the development and preliminary results of new designed C2-symmetric bis-hydroxamic acid (BHA) ligands were described and the application of the new ligands for vanadium-catalyzed asymmetric epoxidation of allylic alcohols as well as homoally-alignated alcohols.
Abstract: In this article, we describe the development and preliminary results of our new designed C2-symmetric bis-hydroxamic acid (BHA) ligands and the application of the new ligands for vanadium-catalyzed asymmetric epoxidation of allylic alcohols as well as homoallylic alcohols. From this success we demonstrate the versatile nature of BHA in the molybdenum catalyzed asymmetric oxidation of unfunctionalized olefins and sulfides.
3 citations
TL;DR: For elderly patients, comparable results can be expected using CB, which opens more opportunity for elderly patients to undergo allogeneic transplants who generally have difficulty finding healthy related donors compared to younger patients.
TL;DR: A number of new synthetic methods are reviewed in this article, most of which are based on aluminum, boron, tin, silver Lewis acids and/or Bronsted acid catalysts.
Abstract: A number of new synthetic methods are reviewed. Most of the methods are based on aluminum, boron, tin, silver Lewis acids and/or Bronsted acid catalysts. Concepts of combined acid catalysis and super Bronsted acid catalysis are also summarized. These methods are useful for selective organic transformations including simple natural product synthesis.