Allylic and Allenic Halide Synthesis via NbCl<sub>5</sub>- and NbBr<sub>5</sub>-Mediated Alkoxide Rearrangements
作者:P. C. Ravikumar、Lihua Yao、Fraser F. Fleming
DOI:10.1021/jo901287f
日期:2009.10.2
Addition of NbCl5 or NbBr5 to a series of magnesium, lithium, or potassium allylic or propargylic alkoxides directly provides allylic or allenic halides. Halogenation formally occurs through a metalla-halo-[3,3] rearrangement, although concerted, ionic, and direct displacement mechanisms appear to operate competitively. Transposition of the olefin is equally effective for allylic alkoxides prepared
将NbCl 5或 NbBr 5 添加到一系列镁、锂或钾的烯丙基或炔丙基醇盐中直接提供烯丙基或烯丙基卤化物。卤化通过金属-卤-[3,3] 重排正式发生,尽管协同、离子和直接置换机制似乎具有竞争性。烯烃的转位对于通过亲核加成、去质子化或还原制备的烯丙基醇盐同样有效。实验上,五卤化铌卤化反应迅速,萃取后可提供基本纯的 ( E )-烯丙基或烯丙基卤化物,适用于一系列脂肪族和芳香族醇、醛和酮。
Intermolecular Tandem Addition−Cyclization of Bromoallenes: A Facile Synthesis of Methylenecyclopropyl Carboxylates and Polysubstituted Furans
作者:Lubin Xu、Xian Huang、Fangrui Zhong
DOI:10.1021/ol061993u
日期:2006.10.1
The base-mediated reactions of 1,3-dicarbonyl compounds with bromoallenes used as an allyl dication equivalent were explored. The corresponding dimethyl methylenecyclopropane-1,1-dicarboxylates and 2,3,4-trisubstituted furans were efficiently synthesized.