Enantioselective epoxidation of conjugated dienes and enynes. Trans-epoxides from cis-olefins
作者:Nam Ho Lee、Eric N. Jacobsen
DOI:10.1016/0040-4039(91)80212-o
日期:1991.11
Asymmetric epoxidation of conjugated dienes and enynes catalyzed by (salen)Mn(III) complex 1 takes place with high chemoselectivity to afford monoepoxides exclusively. Reactions of cis-enynes proceed with very high levels of asymmetric induction, with trans-alkynyl epoxides as the major products.
The new iridium(I)-guanidinate complex served as an efficient catalyst for phosphine-dependent selective cross-dimerization between silylacetylene and terminal alkyl- or arylacetylene. Especially, in case of cross-dimerization between silylacetylene and alkylacetylene, E/Z selectivity of resulting enynes could be controlled by changing phosphine.
The rearrangement of acetylenic epoxidesmediated by low-valence organotitanium and organozirconium reagents is reported to give conjugated enynes. Moderate to good yields and high selectivities are obtained when using the organozirconium(II) Negishi reagent in toluene at 20 °C; whereas only poor yields and low selectivities are achieved with the organotitanium(II) Sato reagent. The process is stereospecific
据报道,由低价有机钛和有机锆试剂介导的炔属环氧化物的重排得到共轭烯炔。在 20 °C 的甲苯中使用有机锆 (II) Negishi 试剂时,可获得中等至良好的产率和高选择性;而使用有机钛 (II) Sato 试剂只能实现低产率和低选择性。该过程是立体有择的,包括通过将低价钛和锆试剂氧化插入到炔环氧化物的碳碳三键中来形成二氧化钛和氧化锆环丙烯。这些金属环丙烯然后通过环氧化物开环重排以提供立体定义的炔丙基金属。共轭烯炔最终通过金属氧化物的β-消除产生。
Stereoselective carbonyl-olefination via organosilicon compounds
作者:Y. Yamakado、M. Ishiguro、N. Ikeda、H. Yamamoto
DOI:10.1021/ja00408a049
日期:1981.9
Accessing Z‐Enynes via Cobalt‐Catalyzed Propargylic Dehydrogenation
作者:Alexandra K. Bodnar、Timothy R. Newhouse
DOI:10.1002/anie.202402638
日期:2024.6.21
Alkenes constitute an enabling motif in organic synthesis, as they can be functionalized to form highly substituted molecules. Z‐alkenes are generally challenging to access due to the thermodynamic preference for the formation of E‐alkenes compared to Z‐alkenes. Dehydrogenation methodologies to selectively form Z‐alkenes have not yet been reported. Herein, we report a Z‐selective, propargylic dehydrogenation that provides 1,3‐enynes through the invention of a Co‐catalyzed oxidation system. Observation of a kinetic isotope effect (KIE) revealed that deprotonation of the propargylic position is the rate limiting step. Additionally, isomerization experiments were conducted and confirmed that the observed Z‐selectivity is a kinetic effect. A proposed stereomechanistic model for the Z‐selectivity is included.