A new procedure for highly stereoselective and regioselective synthesis of 2-ethynyl-3-hydroxytetrahydropyran derivatives based on alkyne-Co2(CO)6 complex
cis-2-ethynyl-3-hydroxytetrahydropyran derivatives via endo mode cyclization pathway. cis-Congeners, cis-3 afforded the corresponding trans tetrahydropyran derivatives exclusively. This novel cyclization has been found to proceed with retention of configuration at the propynyl stereogenic center. Requirement for stereoselectivity in cyclization was discussed.
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.