Showing papers by "Hisashi Yamamoto published in 2016"
TL;DR: The new Lewis- or Brønsted-acid-catalyzed super-silyl-directed AR processes chronicled in the laboratories have come to maturity and now offer a "road map" for strategic stereoselective synthesis of polyketide-like units.
Abstract: ConspectusSince the discovery of the Mukaiyama aldol reaction more than 40 years ago, several landmark publications have inspired researchers in the field. The Mukaiyama AR is one of the most significant named reactions in organic synthesis. In the past few decades, development of the modern AR has been at the forefront in addressing the challenges of regio-, chemo-, diastereo-, and enantioselectivity in organic synthesis. All of these selectivity challenges maybe present in a single pair of reactants, thus controlling the outcome of such a process has great practical value.More than 10 years ago, our group became involved in this iconic carbon–carbon bond-forming process and attempted to very closely investigate all possible features of the AR to solve several issues still encountered by chemists, most notably the selectivity challenges mentioned above. In this context, our group initiated the second generation of the AR based on a Lewis or Bronsted acid-catalyzed process in conjunction with the use of a...
59 citations
TL;DR: The chemoselective amidation strategy can be extended to the catalytic synthesis of dipeptide derivatives, which remains challenging research subjects in modern organic synthesis.
Abstract: We describe herein a new strategy for the chemoselective synthesis of amides by using a metal-catalyzed hydroxy-directed reaction. A hydroxy group located at the β-position of an ester group promoted the activation of a carbonyl group with a tantalum alkoxide catalyst followed by amidation reactions, leading to a wide variety of β-hydroxyamides with excellent chemeselectivity. The chemoselective amidation strategy can be extended to the catalytic synthesis of dipeptide derivatives, which remains challenging research subjects in modern organic synthesis.
56 citations
TL;DR: A new BINOL-derived chiral phosphoric acid bearing 2,4,6-trimethyl-3,5-dinitrophenyl substituents at the 3,3'-positions was developed and applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo- and enantioselectivity.
Abstract: A new BINOL-derived chiral phosphoric acid bearing 2,4,6-trimethyl-3,5-dinitrophenyl substituents at the 3,3'-positions was developed. The utility of this chiral phosphoric acid is demonstrated by a highly enantioselective (ee up to >99 %) and diastereoselective (syn/anti up to >99:1) asymmetric Mukaiyama-Mannich reaction of imines with a wide range of ketene silyl acetals. Moreover, this method was successfully applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo- and enantioselectivity. Significantly, BINOL-derived N-triflyl phosphoramide constitutes a complementary catalyst system that allows the title reaction to be applied to more challenging imines without an N-(2-hydroxyphenyl) moiety.
40 citations
TL;DR: The long-standing problem of the chiral phosphoric acid-catalyzed asymmetric Mukaiyama-Mannich reaction that requires a 2-hydroxyphenyl moiety was solved by this disulfonimide catalyst.
18 citations
TL;DR: In this paper, a highly diastereoselective approach for the synthesis of protected α,β-dioxyaldehydes derived from (Z)-tris(trimethylsilyl) silyl enol ethers is described.
Abstract: A highly diastereoselective approach for the synthesis of protected α,β-dioxyaldehydes derived from (Z)-tris(trimethylsilyl)silyl “super silyl” enol ethers is described. A general and highly syn-stereoselective aldol reaction directed by the “super silyl” group catalyzed by triflimide (HNTf2) is developed providing α,β-dioxyaldehydes and 1,2,3-triol fragments which can be a useful platform for the elaboration of natural and unnatural sugar derivatives.
16 citations
TL;DR: The method was further extended to the kinetic resolution of racemic γ-amino alcohols with a preexisting stereocenter, giving an important class of enantioenriched building blocks that are otherwise difficult to synthesize.
Abstract: Direct asymmetric synthesis of N-chiral amine oxides was accomplished (up to 91:9 e.r.) by means of a bimetallic titanium catalyst. A hydroxy group situated at the γ-position of the N stereocenter enables the desired N-oxidation through dynamic kinetic resolution of the trivalent amine substrates. The method was further extended to the kinetic resolution of racemic γ-amino alcohols with a preexisting stereocenter, giving an important class of enantioenriched (up to 99.9:0.1 e.r.) building blocks that are otherwise difficult to synthesize.
15 citations
TL;DR: Arylamines have been found to generate an N-halo arylamine intermediate, which acts as a highly reactive but selective catalytic electrophilic halogen source as discussed by the authors.
Abstract: Electrophilic halogenation is used to produce a wide variety of halogenated compounds. Previously reported methods have been developed mainly using a reagent-based approach. Unfortunately, a suitable "catalytic" process for halogen transfer reactions has yet to be achieved. In this study, arylamines have been found to generate an N-halo arylamine intermediate, which acts as a highly reactive but selective catalytic electrophilic halogen source. A wide variety of heteroaromatic and aromatic compounds are halogenated using commercially available N-halosuccinimides, for example, NCS, NBS, and NIS, with good to excellent yields and with very high selectivity. In the case of unactivated double bonds, allylic chlorides are obtained under chlorination conditions, whereas bromocyclization occurs for polyolefin. The reactivity of the catalyst can be tuned by varying the electronic properties of the arene moiety of catalyst.
9 citations
TL;DR: In this article, a highly diastereoselective approach for the synthesis of protected α,β-dioxyaldehydes derived from (Z)-tris(trimethylsilyl) silyl enol ethers is described.
Abstract: A highly diastereoselective approach for the synthesis of protected α,β-dioxyaldehydes derived from (Z)-tris(trimethylsilyl)silyl “super silyl” enol ethers is described. A general and highly syn-stereoselective aldol reaction directed by the “super silyl” group catalyzed by triflimide (HNTf2) is developed providing α,β-dioxyaldehydes and 1,2,3-triol fragments which can be a useful platform for the elaboration of natural and unnatural sugar derivatives.
8 citations
2 citations
TL;DR: In this article, the Cu-catalyzed Diels-Alder reaction of 1,3-dienes with nitroso compounds bearing a pyrimidine or pyrazine substituent was achieved with high enantioselectivities using DTBM-Segphos as ligand.
Abstract: The Cu-catalyzed Diels—Alder reaction of 1,3-dienes with nitroso compounds bearing a pyrimidine or pyrazine substituent is achieved with high enantioselectivities using DTBM-Segphos as ligand.
2 citations
TL;DR: In this paper, a chiral tethered 8-quinolinol-based ligand class was developed, and the binuclear titanium complex of the ligand operates through a novel mechanism allowing for the regio-and stereoselective epoxidation of primary and tertiary homoallylic alcohols (up to 98% ee).
Abstract: A new chiral tethered 8-quinolinol-based ligand class is developed. The binuclear titanium complex of the ligand operates through a novel mechanism allowing for the regio- and stereoselective epoxidation of primary and tertiary homoallylic alcohols (up to 98% ee), as well as first examples of 2-allylic phenols (up to 92% ee). The new catalyst system also promotes the asymmetric oxidation of γ-hydroxypropyl sulfides giving an important class of chiral sulfoxides that have been inaccessible to date (up to 95% ee).
TL;DR: The data indicated that allo-HSCT could overcome the poor prognosis of FLT3-mutated AML even for those in non-remission status, despite the profound chemo-resistant character of FLt3- mutant AML.
TL;DR: In this article, a virtually complete enantioselective synthesis of 3-amino-1,2-diols with three consecutive stereocenters was accomplished by a sequential cascade of two kinetic resolutions.
Abstract: A virtually complete enantioselective synthesis of 3-amino-1,2-diols with three consecutive stereocenters was accomplished by a sequential cascade of two kinetic resolutions, which features a Sharpless or Hafnium-catalyzed asymmetric epoxidation and a subsequent W-catalyzed aminolysis. Enantiopure products with up to >99.9% ee and >99.9 : 0.1 dr were obtained and could serve as potential building blocks for pharmaceutical or biological significant molecules.
TL;DR: The cutoff value for distal motor latency (DML) at which sensory nerve action potentials (SNAPs) are absent in carpal tunnel syndrome (CTS) patients was examined retrospectively to elucidate the most discriminative cutoff value.
TL;DR: In this article, a new axially chiral oxazaborolidine catalyst was developed, which consists of a chiral boronic acid and an easily modifiable achiral amino alcohol.
Abstract: A new axially chiral oxazaborolidine catalyst has been developed. This catalyst consists of a chiral boronic acid and an easily modifiable achiral amino alcohol. It could be applied to a Diels–Alder reaction to give the corresponding adduct with good enantioselectivity. Additionally, the bis(oxazaborolidine) catalyst, bearing two Lewis acidic centers enabled a Diels–Alder reaction with higher enantioselectivity.
TL;DR: A BINOL-derived chiral phosphoric acid bearing 2,4,6-trimethyl-3,5-dinitrophenyl substituents at the 3,3'-positions was developed in this article.
Abstract: A new BINOL-derived chiral phosphoric acid bearing 2,4,6-trimethyl-3,5-dinitrophenyl substituents at the 3,3'-positions was developed. The utility of this chiral phosphoric acid is demonstrated by a highly enantioselective (ee up to >99 %) and diastereoselective (syn/anti up to >99:1) asymmetric Mukaiyama-Mannich reaction of imines with a wide range of ketene silyl acetals. Moreover, this method was successfully applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo- and enantioselectivity. Significantly, BINOL-derived N-triflyl phosphoramide constitutes a complementary catalyst system that allows the title reaction to be applied to more challenging imines without an N-(2-hydroxyphenyl) moiety.
TL;DR: The second generation of the Mukaiyama aldol reaction was initiated by as mentioned in this paper based on a Lewis or Bronsted acid-catalyzed process in conjunction with the use of a...
Abstract: ConspectusSince the discovery of the Mukaiyama aldol reaction more than 40 years ago, several landmark publications have inspired researchers in the field. The Mukaiyama AR is one of the most significant named reactions in organic synthesis. In the past few decades, development of the modern AR has been at the forefront in addressing the challenges of regio-, chemo-, diastereo-, and enantioselectivity in organic synthesis. All of these selectivity challenges maybe present in a single pair of reactants, thus controlling the outcome of such a process has great practical value.More than 10 years ago, our group became involved in this iconic carbon–carbon bond-forming process and attempted to very closely investigate all possible features of the AR to solve several issues still encountered by chemists, most notably the selectivity challenges mentioned above. In this context, our group initiated the second generation of the AR based on a Lewis or Bronsted acid-catalyzed process in conjunction with the use of a...