Tamiko Takahashi

Asymmetric 1,3-dipolar cycloaddition of chiral sulphinylethenes with 1-methyl-3-oxido-pyridinium and some nitrones

Abstract 1,3-Dipolar cycloaddition of ( R )-(+)-p-tolyl vinyl sulphoxide 1 with 1-methyl-3-oxidopyridinium 6 proceeded in a diastereoselective manner to afford the exo and endo cycloadducts 11a,b and 12a in 36%, 7% and 29% yield, respectively. The absolute configuration of 11a was determined by its transformation to (1 S )-(−)-2α-tropanol (−)- 15 . Attempts to the cycloaddition of the sulphinylethenes 17–19 with the pyridinium 6 were nsuccessful under several conditions. The reaction of the sulphoxide 20 with pyrroline 1-oxide 21 gave an inseparable mixture of products. The cycloaddition of 20 with 3,4,5,6-tetrahydropyridine 1-oxide 22 afforded a mixture of four adducts in ca. 90% yield. High level of diastereoselectivity was achieved for the endo cycloaddition affording the adduct 23 in 33% isolated yield. The absolute configuration of 23 was confirmed by a single-crystal X-ray diffraction study. The stereochemical course of the reaction was discussed based on the absolute configuration of the products.

Enantioface-differentiating protonation with chiral γ-hydroxyselenoxides

Abstract Enantioface-differentiating protonation of achiral metal enolates of α-alkylcarbonyl compounds 7 has been developed using chiral γ-hydroxyselenoxides 1 as a proton source. Reaction of zinc bromide enolates of 2-benzyl- and 2- n -propylcyclohexanones with (S Se - 1e gave ( S )-2-benzylcyclohexanone 7a and ( R )-2- n -propylcyclohexanone 7c in high enantiomeric excess, respectively. Intramolecular hydrogen bonding of the selenoxide 1 , chelation effects between 1 and metal enolate, and 2- exo -hydroxy-10-bornyl-framework could contribute to this asymmetric induction.

Enantioselective synthesis of carbocyclic showdomycin derivative via asymmetric diels-alder reaction of (Ss)-3-(2-pyridylsulphinyl)acrylate

Abstract The first enantioselective synthesis of a carbocyclic analogue of showdomycin, 3-[(1S,2S,3R,4R)2,3-(isopropylidenedioxy)-4-(pivaloxymethyl)cyclopentyl]maleimide 1 , has been accomplished using the asymmetric Diels-Alder reaction of the (S s )-3-(2-pyridylsulphinyl)acrylate 2 with cyclopentadiene as the key step.

First synthesis of optically pure selenuranes and stereoselective alkaline hydrolysis. Their application to asymmetric [2,3] sigmatropic rearrangement of allylic selenoxides

Abstract The first synthesis of optically pure selenuranes 1 has been accomplished by utilizing 2-exo-hydroxy-10-bornyl group as a chiral ligand. Complete retention of the configuration has been observed in alkaline hydrolysis of 1 to give selenoxides 2. The structure of 1 and 2 has been fully established by X-ray crystallography. [2,3] Sigmatropic rearrangement of allylic selenoxides 2 gave the corresponding allylic alcohols 3 with up to 88% enantiomeric excess (ee). The [2,3] sigmatropic rearrangement of allylic selenoxides 2 progresses predominantly via an endo transition state.

Synthesis of thioaldehydes having optically active alkoxy moiety and their asymmetric hetero Diels-Alder reaction

Optically active α-alkoxycarbonylthioaldehydes (2a-g) were prepared using 8-arylmenthols as chiral auxiliaries. Their asymmetric hetero Diels-Alder reactions with cyclopentadiene gave the endo cycloadducts (3 and 4) and exo cycloadducts (5 and 6) with moderate diastereomeric excesses. However, the major endo cycloadducts (3b-g) were isolated in optically pure form. This is the first chiral synthesis of 2-thiabicyclo[2.2.1]hept-5-ene ring system. The absolute configuration of the cyclic carbonate (12), which was prepared from the major endo cycloadduct (3c) via the epimerization, or the minor exo compound (6c), was determined as 1R by X-ray analysis. The cycloadduct (3c) was transformed to a potential intermediate (14) for the synthesis of carbocyclic homonucleosides

First synthesis and structure of optically pure Te-chiral-alkoxytelluranes

Abstract The first synthesis and isolation of optically pure Te-chiral-alkoxytelluranes 1 and 8 have been developed using the 2- exo -hydroxy-10-bornyl group as a chiral ligand. A distorted trigonal bipyramidal (TBP) structure of 1i with R configuration was confirmed by the X-ray analysis.

A new synthetic approach to pseudo-sugars by asymmetric Diels–Alder reaction. Synthesis of optically pure pseudo-β-D-mannopyranose, 1 -amino-1 -deoxypseudo-α-D-mannopyranose and pseudo-α-L-mannopyranose derivatives

Synthesis of the optically pure title compounds has been achieved. The key features involved (i) construction of 7-endo-oxabicyclo[2.2.1 ]hept-5-ene-2-carboxylates 3 and 9a by the asymmetric Diels–Alder reaction of (S)s-3-(2-pyridylsulphinyl)acrylate 1 with furans 2 and 8; (ii) stereoselective introduction of a 5,6-exo or -endo diol function to give the protected exo diol 4 and the protected endo diol 10, respectively; (iii) formation of the shikimate derivatives 5 and 11 by cleavage of the oxide bridge of compounds 4 and 10; (iv) conversion of compounds 5 and 11 to the pseudo-sugars 6 and 12, and the pseudo-amino-sugar 7.

CFTA, a new efficient agent for determination ofabsolute configurations of chiral secondary alcohols

The CFTA method using α-cyano-α-fluoro-p-tolylacetic acid (CFTA) can be reliable in assigning absolute configurations of chiral secondary alcohols based on both 1H and 19F NMR spectroscopy, and the most stable and most predominant conformer of the CFTA esters that can explain the 1H and 19F NMR data were supported by X-ray analysis and ab initio calculations.

Synthesis of E- and Z-α-fluorourocanic acids as potential inhibitors of urocanase

Abstract Reaction of 1-trityl-4-imidazole carboxaldehyde with triethyl 2-fluoro-2-phosphonoacetate produced an E/Z mixture of ethyl 2-fluoro-3-(1-triphenylmethylimidazol-4-yl] -2-propenoates ( 1a,b ). After separation of the geometric isomers, acid hydrolysis produced the corresponding urocanic acids ( 2a,b ). Neither isomer was a substrate or inhibitor of urocanase.

Preparation of optically active 1,3,2-oxathiaphosphorinanes using (-)-10-mercaptoisoborneol as a chiral source

Optically active 1,3,2-oxathiaphosphorinanes were prepared from (-)-10-mercaptoisoborneol and phosphorus dichlorides [RP(X)Cl 2 ]. The configuration at phosphorus in these derivatives was assigned on the basis of their 1 H nmr spectral data and X-ray diffraction analysis of 4f