In the presence of samarium diiodide and a proton donor (tert-butanol or phenol), δ-oxo-γ,γ-disubstituted-alkylidenemalonates readily cyclise according to the 3-exo-trig mode to give, depending on the exact nature of the substrate, trans and cis cyclopropanols or lactones derived from the cis isomers. Total stereoselectivity towards the formation of trans cyclopropanols is observed with di-tert-butyl alkylidenemalonates when PhOH is used as the protonating agent.
在
镧二
碘和质子供体(如
叔丁醇或
酚)的存在下,δ-氧-γ,γ-二取代烯基
马来酸酯易于按照3-exo-trig模式环化,生成的产物取决于底物的具体性质,可能是反式和顺式
环丙醇或源自顺式异构体的内酯。当使用
酚作为质子化剂时,二叔丁基烯基
马来酸酯对反式
环丙醇的形成表现出完全的立体选择性。