Diels−Alder reactions of cyclic isoimidium salts are described. The corresponding cycloadducts are obtained with high regio- and stereoselectivity. The use of homochiral cyclic isoimidium salts delivers cycloadducts with excellent diastereoselectivity (>99:1) that can be efficiently converted to enantiomerically pure lactones.
Correlations between carbon-13 nuclear magnetic resonance chemical shifts and reactivities of siloxybutadienes and siloxyazabutadienes in the Diels-Alder reaction with dimethyl acetylenedicarboxylate.
In the reaction of silylated butadiene derivatives (1) with dimethyl acetylenedicarboxylate (DMAD), it is proposed that the reactivities of the dienes can be predicted from the carbon-13 nuclear magnetic resonance chemical shifts of the terminal methylene carbons (δ13C-4) of the dienes based on the following linear relationships, a) total electron densities against δ13C-4; b) ln k against 1/[ELUMO(DMAD)-EHOMO(diene)]; c) ln k against δ13C-4. The total electron densities and energy levels of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of the dienes were calculated by the modified neglect of diatomic overlap (MNDO) method.
在硅烷化丁二烯衍生物 (1) 与乙炔二甲酸二甲酯(DMAD)的反应中,建议根据二烯末端亚甲基碳(δ13C-4)的碳-13 核磁共振化学位移,按照以下线性关系预测二烯的反应活性:a) 总电子密度与δ13C-4 的关系;b) ln k 对 1/[ELUMO(DMAD)-EHOMO(二烯)]; c) ln k 对 δ13C-4。二烯的总电子密度以及最高占位分子轨道(HOMOs)和最低未占位分子轨道(LUMOs)的能级是通过修正的忽略二原子重叠(MNDO)法计算得出的。
Synthesis of Amphimedine, a New Fused Aromatic Alkaloid from a Pacific Sponge, Amphimedon sp.