2-(2-Tetrahydrofurylidene)propionates, usually obtained only in the more stable (E) configuration 1, were efficiently isomerised into their (Z) isomers 2 by use of Lewis acids or metallated bases. The (E)/(Z) isomerisation was governed by different factors (type of chelating agent, nature and steric demand of the α,β-unsaturated group). We demonstrated that judicious selection of the α,β-unsaturated
通常仅以更稳定的(E)构型1获得的2-(2-
四氢呋喃基)
丙酸酯通过使用
路易斯酸或
金属化碱被有效地异构化为它们的(Z)异构体2。(E)/(Z)异构化受不同因素控制(
螯合剂类型,α,β-不饱和基团的性质和空间需求)。我们证明,与
LDA [R = N(Me)2,t Bu]或MgBr 2和ZnI 2结合使用,明智地选择α,β-不饱和基团与
螯合剂结合可提供高达95%的产率(R = OBn),并且该反应也受到1,3-
烯丙基菌株的影响。(©Wiley-
VCH Verlag GmbH,69451 Weinheim,Germany,2002)