Sho Yamaguchi

Copper-diphosphine complex catalysts for N-formylation of amines under 1 atm of carbon dioxide with polymethylhydrosiloxane

N-formylation of a wide range of amines proceeded using copper-diphosphine complexes as homogeneous catalysts with polymethylhydrosiloxane (PMHS) under 1 atm of CO2. In the reaction of piperidine, for example, the turnover number (TON) reached 11 700 in 23 h with 90% yield of the formylated product. This TON value is much higher than those of the reported catalysts for the formylation of amines under 1 atm of CO2 with hydrosilanes. The Cu complexes with phosphines having ortho-phenylene structures acted as good ligands for the formylation, as compared to a bidentate ligand connected with a propyl chain and a monodentate ligand. Among these diphosphines, ligands with alkyl functionalities, such as isopropyl and cyclohexyl groups, produced better results than the phenyl group. Not only cyclic secondary amines, but also linear secondary amines and aromatic and aliphatic primary amines were found to be reactive substrates. In the case of 2,2,6,6-tetramethylpiperidin-4-amine, the formylation proceeded regioselectively. A catalytic reaction pathway was proposed from a separate experiment using [Me2NCO2][Me2NH2].

Combinatorial Synthesis of Deoxyhexasaccharides Related to the Landomycin A Sugar Moiety, Based on an Orthogonal Deprotection Strategy

In this report, we describe the stereoselective synthesis of a combinatorial library comprised of 16 deoxyhexasaccharides that are related to a landomycin A sugar moiety, based on an orthogonal deprotection strategy. The use of an olivosyl donor containing a benzyl ether at the C3 position and benzoyl ester at the C4 position, and the olivosyl donor, a naphthylmethyl ether, and a p-nitrobenzylethyl or benzyl sulfonyl ester enabled the synthesis of a set of four diolivosyl units containing a hydroxyl group at the C3 or C4 position by a simple glycosylation and deprotection procedure. Using a phenylthio 2,3,6-trideoxyglycoside, alpha-selective glycosidation proceeded without anomerization of the 2,6-dideoxy-beta-glycosides. In addition, alkylhydroquinone and levulinoyl groups were found to be an effective set of orthogonal protecting groups for the anomeric position and a hydroxyl group. The coupling of all combinations of trisaccharide units in a beta-selective manner was accomplished by activation of the glycosyl imidate with I(2) and Et(3)SiH. No cleavage of the acid-labile 2,3,6-trideoxyglycoside was observed under the conditions used for the reactions. Finally, all of the protected hexasaccharides were deprotected by hydrolysis of the esters, microwave (MW) assisted cleavage of the 2-trimethylsilylethoxymethoxy (SEM) ether, and a Birch reduction.

Mechanistic Studies on the Cascade Conversion of 1,3‐Dihydroxyacetone and Formaldehyde into α‐Hydroxy‐γ‐butyrolactone

The chemical synthesis of commercially and industrially important products from biomass-derived sugars is absolutely vital to establish biomass utilization as a sustainable alternative source of chemical starting materials. α-Hydroxy-γ-butyrolactone is a useful synthetic intermediate in pharmaceutical chemistry, and so novel biomass-related routes for its production may help to validate this eco-friendly methodology. Herein, we report the specific catalytic activity of homogeneous tin halides to convert the biomass-derived triose sugar 1,3-dihydroxyacetone and formaldehyde into α-hydroxy-γ-butyrolactone. A detailed screening of catalysts showed the suitability of tin catalysts for this reaction system, and isotope experiments using [D2]paraformaldehyde, substrate screening, and time profile measurements allowed us to propose a detailed reaction pathway. In addition, to elucidate the activated species in this cascade reaction, the effect of additional water and the influence of additional Brønsted acids on the reaction preferences for the formation of α-hydroxy-γ-butyrolactone, lactic acid, and vinyl glycolate were investigated. The active form of the Sn catalyst was investigated by (119)Sn NMR spectroscopy.

Heterogeneous double-activation catalysis: Rh complex and tertiary amine on the same solid surface for the 1,4-addition reaction of aryl- and alkylboronic acids

Double-activation catalysis by a rhodium complex/tertiary amine catalyst for the 1,4-addition of organoboronic acids was investigated. A rhodium complex and a tertiary amine were co-immobilized on the same silica surface by silane-coupling reactions followed by complexation of the Rh species. Structures of the Rh complex and tertiary amine on the silica surface were determined by solid-state 13C and 29Si MAS NMR, XAFS, and XPS measurements. The immobilized tertiary amine accelerated the Rh-catalyzed 1,4-addition of phenylboronic acid to cyclohexenone. The role of the anchored tertiary amine in the 1,4-addition reaction was clarified by solid-state 11B MAS NMR: it activates the arylboronic acid forming a four-coordinate boron species, which then accelerates the transmetallation step in the Rh complex-catalyzed 1,4-addition. The silica-supported Rh complex/tertiary amine catalyst system could be applicable to the reaction of various aryl- and even alkyl-boronic acids.

A Pd–bisphosphine complex and organic functionalities immobilized on the same SiO2 surface: detailed characterization and its use as an efficient catalyst for allylation

Correction for ‘A Pd–bisphosphine complex and organic functionalities immobilized on the same SiO2 surface: detailed characterization and its use as an efficient catalyst for allylation’ by Ken Motokura et al., Catal. Sci. Technol., 2016, DOI: 10.1039/c6cy00593d.

Influence of the Interaction between a Tin Catalyst and an Accelerator on the Formose‐Inspired Synthesis of α‐Hydroxy‐γ‐butyrolactone

In this study, we focused on the tin‐catalyzed transformation of formaldehyde into α‐hydroxy‐γ‐butyrolactone (HBL) in the presence of an α‐hydroxy carbonyl compound as the accelerator. The screening of various accelerators aided in clarifying the structural prerequisites of the accelerator for the formose‐inspired synthesis of HBL. To investigate the influence of the interactions between the tin metal and the accelerator on the catalytic activity, we performed a deuterium‐exchange experiment with α‐hydroxyacetophenone followed by in situ 119Sn NMR spectroscopy and X‐ray absorption fine structure measurements. On the basis of the experimental results, we proposed a reaction mechanism to obtain HBL.

Co‐Immobilization of a Palladium–Bisphosphine Complex and Strong Organic Base on a Silica Surface for Heterogeneous Synergistic Catalysis

Co‐immobilization of a palladium–bisphosphine complex and a strong organic base, 1,4‐diazabicyclo[2.2.2]octane (DABCO), on a silica support was successfully achieved. The new catalyst structure was characterized by X‐ray photoelectron spectroscopy, solid‐state NMR spectroscopy, X‐ray absorption fine structure spectroscopy, and elemental analysis. Although the local structure of the Pd–bisphosphine complex was unaffected by the presence of DABCO on the same silica surface, its catalytic activity in allylation reactions of nucleophiles was significantly enhanced, achieving turnover numbers (TON) up to >10 000, owing to dual‐activation of substrate molecules by the Pd complex and DABCO.

Mechanistic Insight into a Sugar‐Accelerated Tin‐Catalyzed Cascade Synthesis of α‐Hydroxy‐γ‐butyrolactone from Formaldehyde

Applications of the formose reaction, which involves the formation of sugars from formaldehyde, have previously been confined to the selective synthesis of unprotected sugars. Herein, it is demonstrated that α-hydroxy-γ-butyrolactone (HBL), which is one of the most important intermediates in pharmaceutical syntheses, can be produced from paraformaldehyde. In the developed reaction system, homogeneous tin chloride exhibits high catalytic activity and the addition of mono- and disaccharides accelerates the formation of HBL. These observations suggest that the formose reaction may serve as a feasible pathway for the synthesis of important chemicals.

A Novel Strategy for Biomass Upgrade: Cascade Approach to the Synthesis of Useful Compounds via C-C Bond Formation Using Biomass-Derived Sugars as Carbon Nucleophiles

Due to the depletion of fossil fuels, biomass-derived sugars have attracted increasing attention in recent years as an alternative carbon source. Although significant advances have been reported in the development of catalysts for the conversion of carbohydrates into key chemicals (e.g., degradation approaches based on the dehydration of hydroxyl groups or cleavage of C-C bonds via retro-aldol reactions), only a limited range of products can be obtained through such processes. Thus, the development of a novel and efficient strategy targeted towards the preparation of a range of compounds from biomass-derived sugars is required. We herein describe the highly-selective cascade syntheses of a range of useful compounds using biomass-derived sugars as carbon nucleophiles. We focus on the upgrade of C2 and C3 oxygenates generated from glucose to yield useful compounds via C-C bond formation. The establishment of this novel synthetic methodology to generate valuable chemical products from monosaccharides and their decomposed oxygenated materials renders carbohydrates a potential alternative carbon resource to fossil fuels.

Development of New Carbon Resources: Production of Important Chemicals from Algal Residue

Algal biomass has received attention as an alternative carbon resource owing not only to its high oil production efficiency but also, unlike corn starch, to its lack of demand in foods. However, algal residue is commonly discarded after the abstraction of oil. The utilization of the residue to produce chemicals will therefore increase the value of using algal biomass instead of fossil fuels. Here, we report the use of algal residue as a new carbon resource to produce important chemicals. The application of different homogeneous catalysts leads to the selective production of methyl levulinate or methyl lactate. These results demonstrate the successful development of new carbon resources as a solution for the depletion of fossil fuels.