Author Topic: Li/NH3 enantiomeric questions  (Read 1348 times)

0 Members and 1 Guest are viewing this topic.

KingJacksonV

  • Guest
Li/NH3 enantiomeric questions
« on: August 16, 2001, 05:31:00 PM »
Hey guys,

I wondered if you could clear something up for me.  I keep hearing the use of psudoephedrine as a precursor in the Birch rxn.  I thought reduction of a benzyl alchol via "Birch" yields 99.8 percent straight conversion from one enantiomer of ephedrine to the corresponding+/- enantiomer of N-methyl amphetamine, unracemized (JACS reduction of benzy;).  If this is true, then wouldn't SWIM get active product if he were to start with the + ephedrine salt, instead of the pseudo? 

I'll sleep when I'm dead

Osmium

  • Guest
Re: Li/NH3 enantiomeric questions
« Reply #1 on: August 16, 2001, 05:49:00 PM »
I'm kinda confused about the chiralities of ephedrines and pseudoephedrines right now. But I think the reason is the following: ephedrine and pseudoephedrine have TWO chirality centers, the benzylic position and the carbon to which the amine functionality is connected. When doing a Birch you reduce the benzylic OH, and this chirality center disappears, and only one is left.

hypo

  • Guest
Re: Li/NH3 enantiomeric questions
« Reply #2 on: August 17, 2001, 01:29:00 AM »
yep, pseudoephedrine and ephedrine differ on the -OH carbon. both should give the good stuff.

Man was not born to work.

b159510

  • Guest
Re: Li/NH3 enantiomeric questions
« Reply #3 on: August 17, 2001, 09:11:00 AM »
wouldn't SWIM get active product if he were to start with the + ephedrine salt, instead of the pseudo? ..I believe you will be needing (-)ephedrine.

Back to the Primitive

jim

  • Guest
Re: Li/NH3 enantiomeric questions
« Reply #4 on: August 17, 2001, 12:17:00 PM »
This is in the search engine.  I have posted the correct answer several times.

d-psuedoephedrine  yeilds  d-meth

l-ephedrine yields d-meth

l-psuedo  yeilds l-meth

d-ephedrine  yields l-meth