Stereochemistry of addition of carbanion reagents to `diacetone fructose aldehyde'. Configurational assignment of a 1-deoxyheptulose derivative by X-ray crystallography and NMR studies directed to the assignment of isomeric adducts
作者:Michael J Costanzo、Libuse Jaroskova、Diane A Gauthier、Bruce E Maryanoff
DOI:10.1016/s0957-4166(99)00035-x
日期:1999.2
The addition of carbanionic reagents to `diacetone fructose aldehyde' (6) was investigated with a focus on the stereocontrol. The Grignard reagents, MeMgBr, EtMgBr, i-PrMgBr, and MeMgI, gave a high bias (≥90%) for one diastereomer, assigned as the R-isomer, in ether at −78 to 0°C. The reaction of PhMgBr showed diminished diastereoselectivity under these conditions, with a significant dependence of
研究了向“双丙酮果糖醛”(6)中添加碳负离子试剂,重点是立体控制。格氏试剂MeMgBr,EtMgBr,i- PrMgBr和MeMgI在-78至0°C的乙醚中对一种被指定为R-异构体的非对映异构体具有很高的偏倚(≥90%)。在这些条件下,PhMgBr的反应显示出非对映选择性降低,且异构体比例对温度和溶剂的依赖性很大。PhCH 2 MgBr仅提供了“烯丙基重排”加合物,即13,其非对映异构控制差(约60:40)。MeLi,t -BuLi,PhLi和LiCH 2 CO 2 - t-Bu提供的6-加合物富集了80-89%的R-异构体,而2-lithio-2-ethyl-1,3-dithiane的R:S加合物比例为94:6 (15a:15b)。通过氨基磺酸衍生物2a的X射线分析建立了4a甲醇C1中心的R绝对立体化学。确定了Carbon-13 NMR化学位移标准(C1和C3的化学位移),以促进6的C1加合物的立体化学分配。