Butterfly - 14-1-2010 at 14:22
I need some help with the mechanisms from structure 4 ---> 8 and from 9 ---> 3b. I am totally lost 
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Arrhenius - 14-1-2010 at 15:32
4 to 8 is nucleophilic attack of the amine lone pair on the acid chloride with addition/elimination to liberate a chloride ion which can deprotonate
the ammonium ion to free HCL (hence the base present).
9 to 3b is oxidation of the enamine to the epoxide by oxone, coordination of the epoxide by sodium or potassium, and opening of the epoxide by attack
of methanol followed by a proton transfer. Methanol attacks the more electropositive carbon adjacent to the nitrogen. The epoxide is initally formed
anti to the ester due to unfavorable 1,3-pseudodiaxial interaction if you draw the enamine in the half chair (realistically the diastereoselectivity
is probably poor). Nucleophilic opening of an epoxide must occur with anti-periplanar attack, so the methoxy group is initially "up", but presumably
epimerizes here.
When you don't know a mechanism, the first thing to do is to try and identify a nucleophile and electrophile based on what you know about valence and
electronegativity. Then 1.) make a bond 2.) break a bond 3.) draw the result. That being said, not all reactions involve nucleophiles/electrophiles.
[Edited on 14-1-2010 by Arrhenius]
Butterfly - 15-1-2010 at 02:50
Thank you so much for your complete answer 
But how does the oxone form the
epoxide. I know that the active component of oxone is potassium peroxomomosulfate, KHSO5, but I can't draw the mechanism. Can you help me with that ?
Arrhenius - 15-1-2010 at 06:18
http://en.wikipedia.org/wiki/Potassium_peroxymonosulfate
Just like with organic peroxyacids (e.g. mCPBA), oxone is an <b>electrophilic</b> reagent. So use the double bond as the nucleophile to
attack the peroxide.
A mechanism as shown for mCPBA on wikipedia is probably sufficient. My only concern is that the proton transfer may not be intramolecular - this is
trivial. Anyway, it's better to draw concerted addition of an oxygen atom to the alkene rather than a carbocation (don't draw these unless you have
to).
http://en.wikipedia.org/wiki/MCPBA
[Edited on 15-1-2010 by Arrhenius]
Butterfly - 15-1-2010 at 06:59
Thank you so much. You are an angel