Inter- and Intramolecular [2+2]-Photocycloaddition of Tetronates ? Stereoselectivity, Mechanism, Scope and Synthetic Applications
作者:Michael Kemmler、Eberhardt Herdtweck、Thorsten Bach
DOI:10.1002/ejoc.200400551
日期:2004.11
photocycloaddition reaction (λ = 254 nm, solvent: diethyl ether or tert-butyl alcohol) was carried out in an intramolecular fashion the tri- and tetracyclic products 21−23, 27−36 were obtained in good yields (52−75%) and with excellent simple diastereoselectivity. The reaction tolerates a high degree of substitution at both the tetronate and at the alkene double bond. High facial diastereoselectivities were observed
[2+2]-光环加成反应的各种tetronates (3-8, 12, 16, 20, 37) 已被检查。通过用烷基溴或醇(Mitsunobu 方案)通过O-烷基化,由相应的特电子酸制备四氢呋喃。如果光环加成反应 (λ = 254 nm, 溶剂: 乙醚或叔丁醇) 以分子内方式进行, 三环和四环产物 21-23, 27-36 以良好的产率 (52-75%) 获得) 并具有出色的简单非对映选择性。该反应容许在四氢萘酸酯和烯烃双键处发生高度取代。如果烯烃系链中存在立体中心(例如 7a 33),或者如果烯基取代基连接到四氢呋喃辐照前体的立体 C5 碳原子上(例如 7a 33),则观察到高的面部非对映选择性。G。20 32)。该反应也以分子间方式进行。甲氧基乙氧基甲氧基 (MEM) 保护基团适用于保护游离的四氢萘酸羟基。tetronate 8 与环戊烯的光环加成是高度选择性地以 8:1 的外/内比(59%