4-carboxylate (8) in the ratio 52:9, produced by Diels-Alder cycloaddition of the alkyne to the α,β-unsaturated ester function of the initially-formed 1:1 adduct, the oxanorbornadiene (9), followed by opening of the oxygen bridge and elimination of ethanol. The corresponding reaction involving dimethyl acetylenedicarboxylate gives the expected oxanorbornadiene (5).
                                    丙酸乙酯与3,4-双(三
氟甲基)
呋喃(4)在150°C下反应,得到6,7-双(三
氟甲基)异
香豆素-3-
羧酸乙酯(7)和相应的4-
羧酸酯(8)的混合物)的比例为52:9,这是由
炔烃与最初形成的1:1加合物的氧杂
硼硼烷二烯(9)的α,β-不饱和酯官能团加成Diels-Alder生成的,然后打开氧桥和消除
乙醇。涉及
乙炔二
羧酸二甲酯的相应反应给出了预期的氧杂降
冰片二烯(5)。