Elucidafion of Origin of"Syn-Effect" and Application to Organic Synthesis

用LDA研究了[3-取代(E) -1-丙烯基]氧烷与相应的2,4-二烯醇的1,4消旋开环的立体化学反应。所得2,4 -二烯醇的Z/E比随丙烯基3位取代基的不同而变化。这种现象是基于“syn效应”的概念来讨论的，这个概念主要是由σ→π*相互作用来合理化的。研究了胺与(E) -1-甲酰基- 1,3 -丁二烯亲核加成的立体化学反应。得到的烯丙基砜的Z/E比随胺、溶剂、温度和浓度的变化而变化。当二乙胺在较低浓度和较高温度下反应时，优先得到相应的空间不利的(Z) -4-氨基-2-丁烯基砜。为了实现类似的高(Z)选择性，还研究了亲核加成胺到乙基(E)-2,4-五二酸酯上的立体化学反应，乙基(E)-2,4-五二酸酯具有酯基作为共轭吸电子基代替对甲苯磺酰（Ts）基。在这两种情况下(Z)-异构体的主要形成是由“同构效应”合理化的，这可能主要是由于n/σ→π*相互作用和/或6r-电子同构性。在δ-苯氧基取代的乙烯基氧烷的情况下，[1,2]-Wittig重排在最初的1,4消去环打开后以完全立体选择性的方式得到（E，Z） -2,4-二烯基1,6-二醇。顺序的1,4-消环开环-[1,2]- wittig重排也使用α， α-二甲基烯丙基砜得到相应的(Z)-二烯醇。

Stereochemistry of the 1,4-eliminative ring opening of [3-substituted (E) -1-propenyl]oxiranes to the corresponding 2,4-dienyl alcohols by LDA was investigated. The Z/E ratios of the resulting 2, 4-dienyl alcohols varied with the substituents at 3-position of the propenyl group. This phenomenon was discussed based on the concept of a "syn-effect," which is most primarily rationalized by a σ→π* interaction.Stereochemistry of nucleophilic addition of amines to (E) -1-tosyl-l,3-butadiene was investigated. The Z/E ratios of the resulting allylic sulfones varied with amines, solvents, temperature, and concentration. When diethylamine was reacted in low concentration at higher temperature, the corresponding sterically unfavorable (Z) -4-amino-2-butenyl sulfone was preferentially obtained. Stereochemistry of nucleophilic addition of amines to ethyl (E)-2,4-pentadienoate, which possesses an ester group as a conjugated electron-withdrawing group instead of p-toluenesulfonyl(Ts) group, was also investigated to realize similar high (Z)-selectivity. The predominant formation of (Z)-isomers in both cases was rationalized by a "syn-effect," which might be mainly due to n/σ→π* interaction and/or 6r-electron homoaromaticity.In the case of δ-benzyloxy substituted vinyloxiranes, [1,2]-Wittig rearrangement proceeded following the initial 1,4-eliminative ring opening to give a (E,Z) -2,4-dienyl 1,6-diols in a completely stereoselective manner. The sequential 1,4-eliminative ring opening-[1,2]-Wittig rearrangement also proceeded using α, α-dimethyl allylic sulfones to give the corresponding (Z)-dienyl alcohols.