epimerization occurs at the oxacyclic carbon rather than the benzyl carbon. Diels–Alder reactions of chiral oxacyclic dienes 19 and 22 with maleic anhydride, maleimide and benzoquinone proceeded with high diastereoselectivities, yielding a single cycloadduct efficiently at ambient conditions. The structures of Diels–Alder adducts were determined by 1H NOE NMR spectra. The cycloadducts were formed via the
各种手性氧杂环二烯均经由使用Grubbs催化剂(PCY烯炔复分解合成3)2
氯2 RuCHPh。由(2S)-(苄氧基)-
丙醛制备了一系列带有1,2
-二醇骨架的底物。
乙炔在23°C的CH 2 Cl 2中顺利进行,同时在
乙烯气(1-2.5 atm)下以少量催化剂(2.0 mol%)负载,获得了高收率的产品,且在任何立体异构碳上均未发生差向异构化。加热料5在氮气下,在苯(80℃)中包含双取代
炔烃的化合物导致通过初级产物的差向异构化而形成两个非对映异构体。差向异构化发生在氧杂环碳而不是苄基碳。手性乙二环二烯19和22与
顺丁烯二酸酐,顺
丁烯二
酰亚胺和苯醌的狄尔斯-阿尔德反应具有很高的非对映选择性,在环境条件下可以有效地生成单个环加合物。Diels–Alder加合物的结构由1 H NOE NMR光谱确定。环加合物经由亲二烯体以内模方式与立体异构中心的取代基相反的二烯形成。环加合物29和31将(2S)-