Diels−Alder Reactions of 3-Substituted Coumarins in Water and under High-Pressure Condition. An Uncatalyzed Route to Tetrahydro-6<i>H</i>-benzo[<i>c</i>]chromen-6-ones
作者:Rugiada Girotti、Assunta Marrocchi、Lucio Minuti、Oriana Piermatti、Ferdinando Pizzo、Luigi Vaccaro
DOI:10.1021/jo051539o
日期:2006.1.1
Diels−Alder reactions of 3-substituted coumarins 1a−g with methyl-1,3-butadienes 2a−c carried out in water alone and in CH2Cl2 under 9 kbar pressure are reported. In aqueous medium satisfactory results were obtained by operating at 150 °C, whereas under high pressure the cycloadditions were complete at 60−70 °C with excellent yields (85−95%). The reactions with isoprene (2b) always resulted in the
据报道,在9 kbar的压力下,仅在水中和在CH 2 Cl 2中进行的3-取代香豆素1a - g与甲基-1,3-丁二烯2a - c的狄尔斯-阿尔德反应。在水性介质中,通过在150°C下操作可获得令人满意的结果,而在高压下,环加成反应在60-70°C下完成,收率极高(85-95%)。与异戊二烯(2b)的反应总是导致对环加合物的排他性形成,而与(E)-亚戊二烯(2c)的反应仅检测到邻位产物。3-苯基磺酰基香豆素的环加成(图1A)与(ê)-piperylene (2C)允许内被排他地获得的加合物,而-3-羧基- (1B)与反应2C,得到的混合物的相应的内切/外切加合物以58:42的比例在水中,并在高压条件下以45:55的比例。