The Diels–Alder addition of furan to dimethyl acetylenedicarboxylate (DMAD) affords a monoadduct 1. The position and steric course of further addition of furan to the latter are temperature dependent. At temperatures of 50° or below addition occurs mainly at the activated double bond to give endo-endo4 and endo-exo5 diadducts. At 100° addition occurs at the less substituted double bond of the monoadduct to give analogous endo-endo7 and endo-exo9 diadducts; further addition of furan to the latter at 100° affords four triadducts 12–15. The configurations of all these products were determined by p.m.r. and assignments confirmed by simulation of the spectra.AlCl3 causes enormous rate enhancement of the Diels–Alder additions of furan to DMAD and to the activated double bond of the monoadduct. In the presence of the Lewis acid the predominant diadduct formed is the endo-exo isomer 5.
呋喃与二甲基
乙炔二
羧酸酯(
DMAD)的Diels-Alder加成生成单加合物1。后续的
呋喃加成位置和立体位阻取决于温度。在50℃以下的温度下,加成主要发生在活化的双键上,生成内内型4和内外型5的二加合物。在100℃时,加成发生在单加合物中较不取代的双键上,生成类似的内内型7和内外型9的二加合物;在100℃下,进一步的
呋喃加成形成四种三加合物12-15。所有这些产物的构型都由p.m.r.确定,通过模拟光谱进行确认。
AlCl3可以极大地增强
呋喃与
DMAD以及单加合物上活化的双键的Diels-Alder加成速率。在
路易斯酸的存在下,主要形成内外型异构体5的二加合物。