Control of Regioselectivity and Stereoselectivity in (4 + 3) Cycloadditions of Chiral Oxyallyls with Unsymmetrically Disubstituted Furans
作者:Yunfei Du、Elizabeth H. Krenske、Jennifer E. Antoline、Andrew G. Lohse、K. N. Houk、Richard P. Hsung
DOI:10.1021/jo3011792
日期:2013.3.1
The regioselectivities and stereoselectivities of ZnCl2-catalyzed (4 + 3) cycloadditions between chiral oxazolidinone-substituted oxyallyls and unsymmetrical disubstituted furans have been determined. The substitution pattern on the furan is found to provide a valuable tool for controlling the stereochemistry (endo-I or endo-II) of the 7-membered cycloadduct. While cycloadditions with monosubstituted
已经确定了 ZnCl 2催化的 (4 + 3) 手性恶唑烷酮取代氧基烯丙基和不对称双取代呋喃之间环加成反应的区域选择性和立体选择性。发现呋喃上的取代模式为控制7 元环加合物的立体化学(endo-I或endo-II)提供了有价值的工具。虽然与单取代呋喃的环加成通常有利于内切-I产物,从呋喃添加到氧烯丙基更拥挤的表面,与 2,3- 和 2,5- 二取代呋喃的环加成反而有利于内切-II立体化学。执行密度泛函理论计算以说明选择性。对于单取代呋喃,通过呋喃和恶唑烷酮 4-Ph 基团之间的边对面相互作用稳定导致内-I环加合物的拥挤过渡态,但如果呋喃带有 2 -CO 2 R基团或被2,3-二取代。