Diastereoselectivity of cyclopropanation of substituted α-fluorostyrenes versus styrenes by different methods
作者:Katharina Bartels、Benjamin Schinor、Günter Haufe
DOI:10.1016/j.jfluchem.2017.09.008
日期:2017.11
respectively, were obtained. An advantage of the latter protocol is the in situ formation of ethyl diazoacetate from ethyl glycinate hydrochloride in aqueous solution by diazotation avoiding the in-substance application of the potentially explosive ethyl diazoacetate. Accordingly, a series of diastereoisomeric ethyl 2-aryl-2-fluoro-cyclopropane carboxylates was synthesized from p- or m-substituted α-fluorostyrenes
苯乙烯和α-氟苯乙烯与重氮乙酸酯的环丙烷化的非对映选择性取决于所用催化剂以及氟取代基的存在与否。苯乙烯与重氮乙酸酯的Cu(acac)2催化反应产生3:1的选择性,有利于反式-2-苯基环丙烷羧酸酯,而α-氟苯乙烯则提供了1:1的顺式/反式异构体混合物。竞争实验证明,与苯乙烯本身相比,α-氟苯乙烯的反应更慢。用较大的四苯基铁(III)-卟啉氯化物作为催化剂,分别得到10∶1或3∶1的混合物。后一种协议的优点是原位通过重氮化从水溶液中的甘氨酸乙酯盐酸盐中生成重氮乙酸乙酯,从而避免了潜在爆炸性的重氮乙酸乙酯的实质性应用。因此,非对映异构系列2-芳基-2-氟-环丙烷羧酸的合成自p -或米取代α-氟苯乙烯。