Yasufumi Tamai

Asymmetric [2 + 2] cycloaddition of ketene with aldehydes catalysed by chiral bissulfonamide–trialkylaluminium complexes

Asymmetric [2 + 2] cycloaddition of ketene with the aldehydes 1a–g, catalysed by 10 mol% of C2-symmetric bissulfonamide 2a–c–R3Al complexes afforded optically active 4-substituted oxetan-2-ones 3a–g in up to 74% enantiomeric excess.

Asymmetric [2 + 2] cycloaddition of ketene with aldehydes catalysed by Me3Al complexes of axially chiral 1,1′-binaphthalene-2,2′-diol derivatives

Asymmetric [2 + 2] cycloaddition of ketene 1 with the aldehydes 2a–f, catalysed by axially chiral Lewis acids 3a–c afforded optically active 4-substituted oxetan-2-ones 4a–f in up to 56% enantiomeric excess (e.e.); the stereoselectivity of the reaction depended on the structure of the chiral Lewis acids and of the aldehydes, the order of addition of compounds 1 and 2 and on the solvents employed.

Investigation of the diastereoselectivity in the addition of organometallics to the α-keto esters of axially chiral 1,1′-binaphthalen-2-ol derivatives

The inherent chiral induction abilities of axially chiral 2′-substituted 1,1′-binaphthalen-2-ols 2a-f as the chiral auxiliary for the addition of organometallics to their α-keto acid esters were examined as a function of the following reaction variables: size of the 2′-substituent, nature of the organometallic reagent, solvent, and temperature. In the addition of MeMgl to the phenylglyoxylates 3a-f of the alcohols 2a-f, the corresponding atrolactic acid esters 5a-f and 6a-f were obtained with up to 52% diastereoisomeric excess (d.e.). The preferred diastereoisomer depended on the size of the 2′-substituent, and thus could not solely be determined by the helicity of the 1,1′-binaphthalene framework. By using MeZnl as the nucleophile, the selectivity increased up to 84% d.e. with the same diastereofacial selectivity as that of MeMgl. On the other hand, the diastereofacial selection was reversed when MeTiCl3 was employed as the nucleophile, with low selectivity (14% d.e.).It is concluded that MeMgl or MeZnl, as a nucleophile of low Lewis acidity, adds to the keto ester moiety in the s-trans conformation, while the strong Lewis acid MeTiCl3 mainly adds to the s-cis conformer from the same direction as that of the Grignard addition, thus giving the opposite diastereoisomer.

A highly efficient asymmetric synthesis of a 4,4-disubstituted butan-4-olide by the 1,7-asymmetric inductive addition of Grignard reagents to γ-keto esters

An efficient asymmetric synthesis of a butan-4-olide having a quaternary asymmetric carbon centre was achieved with up to 97% enantiomeric excess (e.e.) by the 1,7-asymmetric inductive addition of Grignard reagents to the γ-keto esters 4–7, the e.e. of which was highly dependent on the structure of the chelating group of the chiral auxiliaries 1–3.

A new approach to remote asymmetric induction in the diastereoselective reduction of γ-keto esters by use of a chiral podand as chiral auxiliary

An efficient 1,7-asymmetric induction was achieved with up to 82% diastereoisomeric excess (d.e.) in the diastereoselective reduction of the γ-keto ester 4 and o-acetylbenzoate 6 using the chiral podand 2 as chiral auxiliary.

Synthesis of Wieland–Miescher ketone analogues bearing an angular protected hydroxymethyl group

Wieland–Miescher ketone analogues (1) and (2), bearing an angular protected hydroxymethyl group, have been prepared by alkylation of the lithiated methyl 2, 6-dimethoxycyclohexa-2, 5-diene-1-carboxylate.

Efficient 1,8- to 1,12-asymmetric induction in Grignard reactions of ω-keto esters by using BINOL or its 2′-oligoether derivatives as the chiral auxiliary

Efficient diastereoselective alkylation of δ- and Iµ-keto acids with Grignard reagents was achieved in up to 97% de by conversion into the 2′-[3-(2-methoxyethoxy)propoxy]-(1,1′-binaphthyl)-2-ol esters, while the corresponding alkylation of ζ- to θ-keto acids could effectively be carried out in up to 88% de by simply using BINOL as the chiral auxiliary.

The absolute stereochemistry of Wieland–Miescher ketone analogues bearing an angular protected hydroxymethyl group

The Wieland–Miescher ketone analogues (3) and (4), each bearing an angular protected hydroxymethyl group, have been prepared by the amino-acid catalysed cyclisation of their cyclohexane-1,3-dione derivatives (1) and (2); the optical purities and absolute configurations of (3) and (4) have been determined by applying the methoxy (trifluoromethyl)phenylacetate method and the c.d. exciton chirality method, respectively, to their mono-9-ol derivatives.

A total synthesis of (+)-pisiferol

A total synthesis of (+)-pisiferol (1) has been accomplished by utilising an optically active Wieland–Miescher ketone analogue (S)-(+)-(6) bearing an angular protected hydroxymethyl group, as the key intermediate. Reductive methylation of the monoacetal (7) of compound (6), followed by Huang–Minlon reduction, gives the trans-decalone acetal (9). Construction of the remaining carbocycle leading to the dodecahydrophenanthrenone (14) is achieved through five sequential reactions (deprotection, methoxycarbonylation, Michael addition with methyl vinyl ketone, demethoxycarbonylation, and intramolecular aldol cyclisation). After introduction of the 2-hydroxypropan-2-yl side-chain, dehydration followed by base-catalysed aromatisation affords pisiferol methoxymethyl ether (18). Finally, hydrolysis furnishes (+)-pisiferol (1).

Polymerization of acetylenic monomer with sulphur dioxide: 2. The microstructure of 1-hexyne, 1-alkenes and sulphur dioxide terpolymers

Abstract Free radical terpolymerization of 1-hexyne (HY), 1-hexene (HE) (or 1-butene) and sulphur dioxide was studied with respect to the microstructure of the terpolymers by means of nuclear magnetic resonance and infrared and ultraviolet spectroscopies. The configuration of the double bond in the main chain was not affected by the presence of the ES (HESO 2 ) unit, but was always trans linkage. A linear correlation between v as(SO) and YS (HYSO 2 ) content in the terpolymers was observed. The mechanism of terpolymer formation is discussed.