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In the presence of a catalytic amount of several trityl salts, 2,3,5-tri-O-benzyl-D-ribofuranose smoothly reacted with alcohols to give various β-ribofuranosides in high yields with high stereoselectivity while reversed stereoselectivity was observed in the coexistence of lithium perchlolate.

Lithium bis[(trifluoromethyl)sulfonyl]imide was found to be a new and effective additive in the stereocontrolled synthesis of α-D-ribofuranosides from 2,3,5-tri-O-benzyl-D-ribofuranose and several alcohols while β-anomers were formed in the absence of the lithium salt. A hypothetical mechanism of this reverse stereocontrol to yield α-D-ribofuranosides by the influence of the lithium salt is discussed.

Convenient method for preparation of 1,2-diamine from the corresponding nitroolefin was established by successive reactions of Michael addition of O-ethylhydroxylamine to nitroolefin and reduction ...

A catalytic enantioselective borohydride reduction of aromatic ketones in presence of 0.1-1 mol% of optically active aldiminato cobalt(II) complex catalysts at 0 °C was successfully achieved using precisely pre-modified borohydride with one equivalent each of tetrahydrofurfuryl alcohol, ethanol and NaBH4. The corresponding secondary alcohols were produced in less than 45 min with high enantiomeric excesses (up to 98% ee). The above method was successfully applied to kinetic and dynamic kinetic resolutions of aromatic ketones.

Nitrosation of various α, β-unsaturated carbonyl compounds with nitrogen monoxide or butyl nitrite was achieved in the presence of silane and a catalytic amount of N, N' -bis (2-ethoxycarbonyl-3- oxobutylidene) ethylenediaminatocobalt (II) complex catalyst. In the presence of a catalytic amount of tris (1, 3-diketonato) iron (III) complex, various terminal and 1, 2-disubstituted olefins were converted into the corresponding nitroso alkane dimers in fairly good yields on treatment with phenylsilane and butyl nitrite.Nitration of various terminal olefins into corresponding nitro olefins were performed on treatment with nitrogen monoxide. Nitroalcohols, minor coproducts, were dehydrated to yield nitro olefins by the subsequent treatment with acidic activated aluminum. By GC analysis, evolution of an equimolar amount of nitrogen gas was observed during the present nitration. A possible reaction pathway including the formation of nitro nitroso compounds, key intermediates, was proposed.

Chiral allylating reagents, readily generated in situ from 2λ2-1,3,2-benzodioxastannole [SnII(O2C6H4)], allyl halides, chiral dialkyl tartrates and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) smoothly react with aromatic aldehydes at −78 °C in the presence of a catalytic amount of copper salts to afford the corresponding homoallylic alcohols in high yields with high enantioselectivities.

Stereoselective C-glycosylation of 2-deoxyribose derivatives having 3-O-thiocarbamoyl directing group with carbon nucleophiles was successfully carried out by using SiCl(OTf)3 as an activator. Several 2-deoxy-β-C-ribofuranosides which can be easily converted to 2′-deoxy-C-nucleosides were obtained in good yields with high stereoselectivities.

Zirconacylopentadiene complex 2c containing gem-dimetallated carbon atoms by zirconium and tin was prepared by the oxidative coupling reaction of ‘Cp2Zr’ with distannyldiyne compounds. Complex 2c having trimethylstannyl groups was characterized by X-ray diffraction and its structure was compared with zirconacyclopentadiene analogues having tert-butyl groups (2a) or trimethylsilyl groups (3). The five-membered zirconacycle ring of 2c has a planar conformation whereas it is twisted in complexes 2a and 3. The C ZrC angle in 2c is smaller than those of the corresponding 2a and 3. The polymerization of ethylene proceeded when these complexes were used in combination with methylaluminoxane and it was found that the catalytic activities of these complexes were remarkably influenced by the substituunts on the α-carbon atoms.

A new efficient method for the catalytic stereoselective synthesis of various α-L-fucosides by using an easily available and stable glycosyl donor, 2,3,4-tri-O-benzyl-L-fucopyranosyl methoxyacetate, is established. Also, trimethylsilyl trifluoroacetate and lithium perchlorate are found to be effective additives in the synthesis of Fucα1-3GlcNAc and Fucα1-4GlcNAc linkages.

The enantioselective borohydride reduction using optically active cobalt(II) complex catalysts was successfully applied to various aryl N-diphenylphosphinyl imines, and the corresponding reduced products were obtained in good yields with high enantiomeric excesses (up to 99% ee). The optically active primary amines were obtained by the successive hydrolysis under mild conditions.

A new and efficient method for catalytic stereoselecive synthesis of several glycosides from thioglycosides is successfully performed by the combined use of trityl salt and sodium periodate. Several β-D-gluco- and galactopyranosides are prepared in good yields with high stereoselectivities.

A new and efficient method for catalytic highly α-selective N- and C-glycosylations of 2-deoxyribose derivative with various trimethylsilylated nucleophiles was successfully developed by utilizing effective remote stereocontrol with 5-O-diethylthio carbamoyl directing group. Several 2′-deoxy-α-ribonucleosides and precursors of its C-analogues were prepared in good yields with high stereoselectivities.

Optically active novel taxoids were efficiently synthesized from 8-membered ring compound 3 by successive constructions of BC and ABC ring systems via each intramolecular aldol and intramolecular pinacol coupling reactions.

Transglycosylation of methyl glycosides with various glycosyl acceptors using a Sn(OTf)2–Me3SiCl promoter system in the presence of molecular sieves 5A afforded the corresponding glycosides. Several useful disaccharides are effectively prepared in good yields with moderate to good stereoselectivities.

The anomerization reactions of several β-D-glucopyranosides proceed smoothly in the coexistence of MgBr2·OEt2 and a catalytic amount of titanium(IV)halides to afford the corresponding α-D-glucopyranosides. The desired alkyl α-glucosides and α-anomer of disaccharides such as Glcα1-6Glc were obtained in high yields with high stereoselectivities.

Chiral allylating reagents, readily generated in situ from tin(II) catecholate [SnII(O2C6H4)], allyl halides, chiral dialkyl tartrates, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), reacted smoothly with aldehydes or reactive ketones at −78 °C in the presence of a catalytic amount of copper salts to afford the corresponding optically active homoallyl alcohols. Allylation of aromatic aldehydes and pyruvates by the present chiral tin reagents proceeded in high yields (81—99%) with high enantioselectivities (89—94%ee). In addition, both enantiomers of dimethyl citramalate were prepared from the allylation products of benzyl pyruvate.

Several 2-deoxy-α-D-glucopyranosides are stereoselectively synthesized in high yields by glycosylation of various alcoholic nucleophiles with 3,4,6-tri-O-benzyl-2-deoxy-glucopyranose using a catalytic amount of trityl tetrakis(pentafluorophenyl)borate.

Optically active 2α,10β-dibenzyloxy-11β-(t-butyldimethylsiloxy)-7β-hydroxy-1α-(4-methoxybenzyloxy)–8β,15,15-trimethyl-4-methylene-trans-bicyclo[6.4.0]dodecan-9-one 2 that corresponds to BC ring system of Taxol was prepared from 8-membered ring enone 3 in high yield via stereoselctive Michael addition and successive intramolecular aldol cyclization. The above 8-membered ring enone 3 was synthesized from the linear optically active polyoxy-compound 4 by SmI2-mediated intramolecular aldol cyclization.

Construction of the AB-ring system of the taxane framework via an A-ring annulation strategy was demonstrated by base-mediated intramolecular aldol reaction of (Z)-2,2-dimethyl-3-(1-methyl-2-oxopropylidene)cyclooctanone, affording the title compound, 1-hydroxy-8,11,11-trimethylbicyclo[5.3.1]undec-7-en-9-one. A cyclization precursor, the tetra-substituted (Z)-alkene, was prepared from the corresponding cyclooctanone derivative, 3-[(alpha,alpha- dimethylbenzyl)dimethylsiloxy]-2,2-dimethylcyclooctanone via a bicyclic alpha,beta-unsaturated lactone intermediate.

Total asymmetric synthesis of Taxol was completed by dehydration condensation between a protected N-benzoylphenylisoserine 4 or 9 and 7-TES baccatin III which was prepared from 8-membered ring enone. Taxol side chains 4, 7, 9 and 11, optically active protected N-benzoylphenylisoserines, were successfully synthesized by enantioselective aldol reaction from two achiral starting materials, benzaldehyde and an enol silyl ether derived from S-ethyl benzyloxyethanethioate.

Baccatin III was efficiently synthesized from the BC ring system of Taxol,2α,10β-dibenzyloxy-11β-(t-butyldimethylsil-oxy)-7β-hydroxy-1α-(4-methoxybenzyloxy)-8β,15,15-trimethyl-4-methylene-trans-bic...

A catalytic and stereoselective glycosylation of glycosyl fluorides with several glucosides is successfully performed by using a catalytic amount of trityl tetrakis(pentafluorophenyl)borate.

An efficient method for the synthesis of (−)-cephalosporolide D was established via successive enantioselective aldol reaction and effective construction of 8-membered ring lactone moiety.

Various carboxylic esters were obtained in high yields from free carboxylic acids and several alcohols including bulky ones by using O,O′-di(2-pyridyl) thiocarbonate and a catalytic amount of DMAP.

A new and efficient method for catalytic stereoselective synthesis of 1,2-trans-glycosides was successfully established by use of 2,3,4,6-tetra-O-p-chlorobenzyl-β-D-glucopyranosyl phenyl carbonate as a stable and easily-available glycosyl donor. Several β-D-glucopyranosides were prepared in good yields with high stereoselectivities.

A new and efficient method for catalytic hydrolysis of thioglycosides was successfully developed. Various thioglycosides were smoothly hydrolyzed to afford the corresponding 1-hydroxy sugars in high yields. The hydrolysis of disaccharides was took place smoothly without accompanying no anomerization of existing glycosidic bond.

The reductive coupling reaction of aromatic and aliphatic ketones including acyclic aliphatic ketones proceeded smoothly to give the corresponding pinacols in good to high yields below room temperature by the combined use of titanium(II) chloride and zinc in the presence of pivalonitrile. Meso-selective formation of the coupling products was observed in the cases with some acyclic aliphatic ketones.

Optically active aldiminato cobalt(II) complexes have been found to catalyze the enantioselective reduction of ketones with sodium borohydride affording the corresponding optically active secondary alcohols in high chemical yields with high enantioselectivities. The enantioselective borohydride reduction is also applicable to not only C=O bonds in aromatic ketones but also to C=N bonds in aromatic imines.

Stereoselective Diels-Alder reaction between several α,β-unsaturated ketones and acetoxy-1,3-butadienes is effectively performed by the promotion of diethylaluminum ethoxide under mild conditions. This reaction is successfully applied to the synthesis of optically active bicyclo[6.4.0]dodecanone 9 which corresponds to the BC ring system of 10-deoxy taxane derivatives from the 8-membered ring enone 7 and diene 2.

Optically active novel 18-demethyltaxiods were successfully synthesized from 2α,10β-dibenzyloxy-11β-(t-butyldimethylsiloxy)-7β-hydroxy-1α-(p-methoxybenzyloxy)-8β,15,15-trimethyl-4-methylene-trans-bicyclo[6.4.0]dodecan-9-one (2) which corresponds to the BC ring system of Taxol by stereoselective allylation and intramolecular aldol condensation reactions.

Crossed aldol reaction of enol esters, stable carbon nucleophiles, with carbonyl compounds is effectively performed by the promotion of diethylaluminum ethoxide under mild conditions. This reaction is applicable not only to simple enol esters but also to lactones such as α-angelicalactone.

Highly diastereoselective aldol reaction of α-bromo ketones with aliphatic aldehydes was successfully carried out by using titanium(II) chloride and copper in dichloromethane at low temperature. Similarly, Reformatsky-type reaction of α-bromo thioester with aliphatic aldehydes was promoted under mild conditions to afford β-hydroxy thioesters in good to moderate yields.

The trityl tetrakis(pentafluorophenyl)borate [TrB(C6F5)4] catalyzed stereoselective synthesis of various disaccharides was successfully carried out by treating a new 2-O-acyl-protected glycosyl donor, 3,4,6-tri-O-benzyl-2-O-p-toluoyl-β-D-glucopyranosyl phenylcarbonate, with several glycosyl acceptors, thioglycosides, affording the corresponding disaccharides in high yields.

New highly effective promoter system for the glycosylation of thioglycoside, the combined use of stoichiometric amount of either N-iodosuccinimide or N-bromosuccinimide and a catalytic amount of TrB(C6F5)4, was developed and was successfully applied to the one-pot sequential synthesis of trisaccharides. In the first glycosylation step, 3,4,6-tri-O-benzyl-2-O-p-toluoyl-β-D-glucopyranosyl phenylcarbonate was treated with thioglycosides in the presence of a catalytic amount of TrB(C6F5)4 alone, and the following glycosylation with methyl α-D-glycosides was carried out by further addition of either N-iodosuccinimide or N-bromosuccinimide to the initially resulted reaction mixture to afford the corresponding trisaccharides in one-pot manner.

Newly utilized low-valent titanium reductant, titanium(II) bromide, was conveniently prepared by treating titanium(IV) bromide with hexamethyldisilane. The pinacol reaction of aromatic and aliphatic aldehydes including primary aldehydes proceeded smoothly in dichloromethane-pivalonitrile at temperatures ranging from −23 to 0 °C by the combined use of soluble titanium(II) bromide and copper to give 1,2-diols in good to high yields with good to high dl-selectivities.

The pinacol coupling reaction of aromatic and aliphatic aldehydes including pivalaldehyde with low valent titanium iodide, in situ formed from titanium iodide(IV) and copper, proceeded smoothly in a mixed solvent of dichloromethane and pivalonitrile to give the corresponding 1,2-diols in good to high yields and dl-selectivities.

Reductive coupling reaction of aromatic and aliphatic aldehydes proceeded under mild conditions to give the corresponding pinacols in moderate to high yields and dl -diastereoselectivities by using combinations of either low valent titanium(II) bromide and copper or titanium(IV) iodide and copper in a mixed solvent of dichloromethane and pivalonitrile. In the case of using titanium(IV) iodide and copper, pinacols were obtained in good to high yields with moderate to high diastereoselectivities irrespective of the number of substitutuents at α-position of aliphatic aldehydes.

High yield and excellent diastereoselectivity in the formation of methyl (2R, 3R, 5R, 6S)-2,6-dibenzyloxy-7-(t-butyldimethylsiloxy)-3-hydroxy-5-(4-methoxybenzyloxy)-4,4-dimethylheptanoate 3 and methyl (2R, 3R, 4S)-2,4-dibenzyloxy-3-hydroxypentanoate 7 are achieved by aldol reaction between (Z)-2-benzyloxy-1-methoxy-1-(trimethylsiloxy)ethene 1 and chiral alkoxy aldehydes using three equivalents of MgBr2·Oet2. The following mechanism of the above aldol reaction proposes that MgBr2·Oet2 activated both chiral alkoxy aldehydes and silyl enolate, that is, magnesiumu enolate, formed by transmetalation from silyl enolate and MgBr2·Oet2, reacted with MgBr2·Oet2-chelated alkoxy aldehydes via the six-membered cyclic transition state.

Unsymmetrical alkyl 2-hydroxy-1-(1-hydroxyalkyl)alkyl ketones (bis-aldols) are successfully synthesized by way of sequential two aldol reactions using α-bromo ketones and two different aldehydes. In the first reaction, α-bromo-β-stannyloxy ketones are formed by tin(II) trifluoromethanesulfornate-promoted aldol reaction of α-bromo ketones with several aldehydes. Bis-aldols are then formed via the second aldol reaction between another aldehydes and dianionic enolates generated by the reduction of α-bromo-β-metalloxy ketones with titanium(IV) iodide and copper.