Thursday, August 16, 2007

benzylic functionalization

1.super base (deprotonation directly)
In hexanes, you get both deprotonation on benzylic and on the benzene ring, selectivity is bad.
Change the solvent to THF, only benzylic deprotonation resulted.

2. activated Zn + benzylic bromide
Zn can be activated by many methods, for example, TMSCl, dibromoethane, HCl or ultrasound, The activation reaction is hard to repeat.
other metal can be added to increase the reactivity of the benzylic anion.(Mn,Cu)

3. benzylic bromide + Mg (barbier type rxn)
works for some particular substrates only.

4. SmI2
ex. benzylic bromide + aldehyde.
barbier type, yield is only 50%, pivaldehyde can be added into the reaction mix to convert the alcohol to ketone in one pot.
using of Sm metal is also described in the literature.

5. Mn

No comments: