Yasuharu Sakamoto

STEREOSELECTIVE SYNTHESES OF CYTOXAZONE, A NOVEL CYTOKINE MODULATOR, AND ITS STEREOISOMERS

Cytoxazone, a novel cytokine modulator, and its stereoisomers were stereoselectively synthesized via stereocontrolled introduction of an azide group and direct construction of the 2-oxazolidinone ring from an azide carbonate by reductive cyclization.

Heterogeneous allylsilylation of aromatic and aliphatic alkenes catalyzed by proton-exchanged montmorillonite.

Allylsilylation of an alkene is the only known procedure to install both silyl and allyl groups onto a carbon-carbon double bond directly. Proton-exchanged montmorillonite showed excellent catalytic performances for the allylsilylation of alkenes. For example, the reaction of p-chlorostyrene with allyltrimethylsilane proceeded smoothly to afford the corresponding allylsilylated product in 95% yield. We also attempted to isolate the reaction intermediate on the montmorillonite surface to investigate the reaction mechanism.

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.

A (3+2)-cycloaddition approach to 1α, 2β, 25-trihydroxyvitamin D3 a ring synthon

Abstract Synthesis of a chiral A-ring model of 1α, 2β, 25-trihydroxyvitamin D 3 by the nitrile oxide cycloaddition and its diastereoselectivity based on MM2 transition state model are described.

Macroring contraction methodology. 6. transannular diels-alder reaction of the 14-members (E,E,E)-trienone

Abstract Transannular Diels-Alder reaction of the 14-membered (E,E,E)-trienone 9 and a discussion of its high diastereoselectivity based on MM2 transition-state model are presented.

A new approach to asymmetric synthesis of Stork's prostaglandin intermediate

Abstract A stereocontrolled approach to assymmetric synthesis of Storks prostaglandin intermediate 3 has been developed which involves the [2,3]-Wittig rearrangement and the Pd(II)-catalyzed allylic acetate rearrangement as the key steps.

STEREOCHEMICAL PREDICTION FOR TANDEM RADICAL CYCLIZATION BASED ON MM2 TRANSITION STATE MODEL. NEW APPROACH TO STEROID CD-RING

Abstract Synthesis of steroid CD-ring by using tandem radical cyclization and its diastereoselectivity based on MM2 transition state model (flexible model) are described.

Experimental and computational studies of the roles of MgO and Zn in talc for the selective formation of 1,3-butadiene in the conversion of ethanol

The one-step conversion of ethanol to 1,3-butadiene was performed using talc containing Zn (talc/Zn) as a catalyst. The influence of the MgO and Zn in the talc on the formation rate and selectivity for 1,3-butadiene were investigated. MgO as a catalyst afforded 1,3-butadiene with a selectivity that was nearly the same as talc/Zn at ∼40% ethanol conversion at 673 K, although the rate of 1,3-butadiene formation over MgO was about 40 times lower than that over the talc/Zn. The introduced Zn cations were located in octahedral sites in place of Mg cations in the talc lattice. The Zn cations accelerated the rate of CH3CHO formation from ethanol, resulting in an increase in the rate of 1,3-butadiene formation. However, the rate of CH3CHO consumption to form crotonaldehyde was not influenced by Zn, although the distribution of crotonaldehyde was decreased with increasing Zn concentrations. X-ray photoelectron spectra of talc/Zn showed that the O1s binding energy was increased by increasing the concentration of Zn, while those of both Mg2p and Si2p were hardly influenced. DFT calculations were used to estimate the atomic charges on the O, Mg, Si, and Zn atoms when an atom of Zn per unit cell of talc was introduced into an octahedral site. On the basis of the results for the conversion of ethanol into 1,3-butadiene and the corresponding DFT calculations, the roles of the O, Zn, Mg, and Si atoms in the talc catalyst for the formation of 1,3-butadiene from ethanol were discussed.

Efficient phthalate-tethered ring-closing metathesis as a cross-coupling reaction

An efficient method for cross-coupling using phthalate-tethered ring-closing metathesis was developed. Based on this method, the stereocontrolled syntheses of both (R,R)- and (S,R)-1-methoxypentadecane-2,9-diol (17, 20) were achieved from (R)-1-undecen-5-ol (4e) and (R)-1-methoxy-5-hexen-2-ol (13).

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.