I am synthesizing the compound 1 by using chan-lam reaction as the figure showing. However, the conversion yield of ortho fluoroboronic acid (less than 20% on LC/MS) is much lower than the para fluoroboronic, which is very strange since the boronic acid is a nucleophile reagent and the F is ortho/para activated substituent and smaller than H in size.
Hi
This is most likely because of steric hindrance for the 2-fluoroboronic acid. You can try heating the reaction.
Why would F be smaller than H?
The atomic radius of H is smaller than F regardless of whether it is measured as an atom or as a covalent bond.
https://en.wikipedia.org/wiki/Atomic_radii_of_the_elements_(data_page)
Could be because of electrostatic repulsion between the fluorine and the nearby oxygen.
Xun
You provided two equations in your question using 2-fluoroboronic acid and 4-fluoroboronic to give the same compound 1.
Is that right?
Also, see the reaction mechanism for Chan-Lam Coupling
https://www.organic-chemistry.org/namedreactions/chan-lam-coupling.shtm
to understand how this reaction goes.
Good luck
Hi;
Steric hindrance (the reaction site is blocked by F and B(OH)2 groups forming part of the molecule).
Best regards
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