Yasuhiro Yamashita 교수

Recent developments in catalytic asymmetric aldol reactions have been summarized. Enantioselective aldol reactions are important methods to synthesize β-hydroxy carbonyl compounds in optical pure form, and as such, numerous successful chiral catalysts were designed and applied for asymmetric aldol reactions. This review article is organized under the categories of: (1) catalytic enantioselective aldol reactions of preformed enolates, (2) catalytic enantioselective direct-type aldol reactions usi

The direct, Ir-catalyzed, regio- and enantioselective amination of allylic alcohols with Lewis acid activators to form branched allylic amine products is reported. The reactions of arylamines, benzylic amines, and secondary aliphatic amines in the presence of Nb(OEt)5 as activator occurred with high regioselectivities and high enantioselectivities. These results led to the development of Ir-catalyzed reactions of allylic alcohol with arylamines and BPh3 as activator in catalytic amounts. These r

Catalytic asymmetric aldol reactions of silyl enol ethers with aldehydes (Mukaiyama aldol reactions) have been performed using novel chiral zirconium catalysts. The reactions proceeded in high yields under mild conditions, and anti-adducts were obtained in high diastereo- and enantioselectivities. The catalysts were first prepared from zirconium(IV) tert-butoxide (Zr(O(t)Bu)(4)), (R)-3,3'-diiodo-1,1'-binaphthalene-2,2'-diol ((R)-3,3'-I(2)BINOL), a primary alcohol, and a small amount of water. It

Catalytic asymmetric hetero Diels-Alder (HDA) reactions using a chiral zirconium complex have been developed. The reactions of aldehydes with Danishefsky's dienes proceeded smoothly to afford the corresponding pyranone derivatives in high yields with high diastereo- and enantioselectivities in the presence of a chiral zirconium complex, which was prepared from zirconium tert-butoxide, (R)-3,3'-diiodobinaphthol or its derivative, a primary alcohol, and a small amount of water. It is noted that 2,

Asymmetric [3+2] cycloaddition of hydrazones to external olefins has been successfully conducted in high yields with high enantioselectivities using a chiral zirconium catalyst. These reactions open ways to synthetically and biologically important pyrazoline, pyrazolidine, and 1,3-diamine derivatives. Further, several experiments suggested that the reactions proceeded via concerted pathways.

Silver lining: Highly exo-selective asymmetric [3+2] cycloaddition of α-amino ester Schiff bases with activated olefins proceeds in the presence of AgHMDS/1. The α-amino ester Schiff bases including those derived from aliphatic imines successfully reacted to afford the corresponding pyrrolidine derivatives in high yield with high exo- and enantioselectivities. EWG=electron-withdrawing group, HMDS=hexamethyldisilazide. Detailed facts of importance to specialist readers are published as ”Supportin

The first catalytic asymmetric [3 + 2] cycloadditions of Schiff bases of alpha-aminophosphonates with olefins have been developed. Chiral silver amide complexes bearing (R)-DTBM-SEGPHOS worked well as catalysts for the first time, and proline phosphonic analogues were obtained in high yields with excellent exo- and enantioselectivities.

We found six bacteria capable of producing antifreeze protein (AFP) from Ross Island, Antarctica. Among these AFP-producing bacteria, strain No. 82 had the highest antifreeze activity and was identified as Moraxella sp. The optimum temperature and pH for the production of AFP were 5 degrees C and 7.0, respectively. After partially purifying the AFP from the culture supernatant using 60% saturation of ammonium sulfate, only the 52-kDa protein band (100 microg/ml) which eluted from SDS-PAGE indica

Catalytic addition reactions of very weakly acidic nonactivated alkylarenes such as toluene and its derivatives were developed by using a strongly basic mixed catalyst system under mild reaction conditions. The addition reactions with imines and alkenes proceeded smoothly under proton-transfer conditions to afford the desired products in good to high yields, and high levels of regio- and stereoselectivity were achieved. It was also revealed that the asymmetric addition reaction of an alkylarene

Recent developments in chiral alkaline-earth metal catalysts are summarized. Alkaline-earth metals are very attractive metal species because they are ubiquitous elements in nature, and form less harmful compounds compared with heavy transition metals. Several types of chiral ligands have been successfully employed for chiral modification of alkaline-earth metal catalysts, and high stereoselectivities have been achieved in asymmetric carbon–carbon bond forming reactions. These remarkable results

The development of catalytic asymmetric carbon-carbon bond-forming reactions of alkylnitriles that do not have an activating group at the α-position, under proton-transfer conditions, is a challenging research topic. Here, we report catalytic asymmetric direct-type 1,4-addition reactions of alkylnitriles with α,β-unsaturated amides by using a catalytic amount of potassium hexamethyldisilazide (KHMDS) with a chiral macro crown ether. The desired reactions proceeded in high yields with good diaste

Brønsted base–photocatalyst hybrid systems have been developed for reactions of malonates with styrene derivatives. The concept of this process lies in the photo-oxidation of catalytic amounts of the enolate to form reactive radicals that react with alkene double bonds under mild reaction conditions. This is an example of visible-light-activated C–C bond formation reactions of malonates with alkenes to realize high atom economy under very mild reaction conditions without using any transition-met

Catalytic amination of silyl enol ethers with azo diester compounds was investigated. It was shown that Cu(OTf) 2 or AgOTf had high catalytic activity and that AgOTf was the most efficient among the catalysts tested in the reactions. In asymmetric reactions, the AgClO 4 -BINAP system showed high enantioselectivity. In a mixture of toluene or mesitylene and THF, silyl enol ethers reacted with dibenzyl azodicarboxylate (DBnAD) smoothly to afford the corresponding amination adducts in excellent yie

[reaction: see text] The first catalytic, asymmetric 2,3-trans-selective hetero Diels-Alder reaction has been developed. The reactions of aldehydes with Danishefsky's dienes proceeded smoothly to afford the pyranone derivatives in high yields with high trans-selectivities and enantioselectivities in the presence of a chiral zirconium complex, which was prepared from zirconium tert-butoxide and (R)-3,3'-diiodobinaphthol or its derivatives, primary alcohol, and a small amount of water. This reacti