Selective Prins Reaction of Styrenes and Formaldehyde Catalyzed by 2,6-Di-<i>tert</i>-butylphenoxy(difluoro)borane
作者:Thorsten Bach、Johannes Löbel
DOI:10.1055/s-2002-35645
日期:——
The sterically congested Lewis acid 1 was used as a catalyst in the Prins reaction of various styrenes and formaldehyde. 4-Aryl-1,3-dioxanes 5 were selectively formed as the exclusive products of the reaction with styrenes 4a-i and vinylthiophenes 4j-k. The reaction proceeded in most cases with good to excellent yields (55-99%). Styrenes which carried a strongly electron-withdrawing group (CN. CO 2
空间拥挤的路易斯酸 1 被用作各种苯乙烯和甲醛的 Prins 反应的催化剂。4-芳基-1,3-二恶烷5 被选择性地形成为与苯乙烯4a-i 和乙烯基噻吩4j-k 反应的唯一产物。在大多数情况下,反应以良好至极好的产率(55-99%)进行。带有强吸电子基团(CN.CO 2 Me)的苯乙烯不发生反应。对于甲基取代的底物 6a,与 β-烷基苯乙烯 6 的反应是成功的,并优先产生 (88%) 反式-5-甲基-4-苯基-1,3-二恶烷 (7a) (dr = 75:25)。由于空间原因,其他 β-烷基苯乙烯 6b-d 没有反应。催化剂 1 获得的显着立体区分被用于将 4-丙烯基苯乙烯 (10) 区域选择性转化为二恶烷 11 (83% 产率)。