87(P77) キラル異方性試薬2NMAを用いたβ-メチル置換およびγ-メチル置換2級アルコールの相対配置および絶対配置の決定について(ポスター発表の部)

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A new methodology using a chiral anisotropic reagent, 2NMA [methoxy-(2-naphthyl)acetic acid] has been developed for determination of absolute configurations of acyclic β- or γ-methyl substituted secondary alcohols. 2NMA is known as a powerful NMR reagent to determine the absolute configuration of a secondary hydroxy group especially on a long C-C chain compound. ^1H-NMR spectra of several model 2NMA esters derived from acyclic β- or γ-methyl substituted secondary alcohols were measured, and the Δδ values (δ_<R-ester>-δ_<S-ester>) for both syn and anti isomers were calculated. We found the significant differences of the |Δδ| values between syn and anti isomers. In the case of β-methyl substituted secondary alcohols, |Δδ| values of each proton at γ- and δ-position for syn compounds are larger than those for and compounds. While, in the case of γ-methyl substituted secondary alcohols, |Δδ| values of each proton at γ-, δ-, ε-, and ζ-position for and compounds are larger than those for syn compounds. Threshold values of |Δδ| between syn and anti have been established; in β-methyl substituted secondary alcohols, 0.35 ppm for γ-position and 0.25 ppm for δ-position, and in γ-methyl substituted secondary alcohols, 0.41, 0.23, 0.28, and 0.15 ppm for γ-, δ-, ε-, and ζ-position, respectively. That is, in the case of β-methyl substituted secondary alcohols, if these |Δδ| values at the γ- and δ-protons are larger than the corresponding threshold numbers, the relative stereochemistry should be assigned as syn. On the contrary, smaller |Δδ| values than the threshold numbers suggest the relative stereochemistry to be anti. In the case of γ-methyl substituted secondary alcohols, these |Δδ| values of protons at γ-, δ-, ε-, and ζ-positions being larger than the corresponding threshold values, the relative stereochemistry should be determined as anti. Smaller |Δδ| values than the threshold numbers show the relative stereochemistry to be syn. The absolute configuration of secondary hydroxy group is easily determined by the sign of each Δδ value as usual, thus, the absolute configurations of both methyl and hydroxyl in the acyclic β- or γ-methyl substituted secondary alcohols could be determined.
天然有機化合物討論会の論文
1998-08-31

87(P77) キラル異方性試薬2NMAを用いたβ-メチル置換およびγ-メチル置換2級アルコールの相対配置および絶対配置の決定について(ポスター発表の部)

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