swibb has also been following the idea thread of exploring the viability of psuedo synthesis. in his studies swibb has found a reference to a method published in the rsc.com website. here's a link to the sample reference
http://www.rsc.org/pdf/molecularworld/alkenesample.pdf
section 4.4 is the section of interest. swibbs in depth knowledge isn't there so he's unsure of how feasible this method even is, but does anyone have access to or already have any of these publications?
108
Reaction 4.13 reviews our progress so far; we have a three-stage route leading from
Z-1-phenylprop-1-ene, via a bromoalcohol and an oxirane, to pseudoephedrine. Yet
Planning the synthesis of pseudoephedrine
(4.13)
H2
H H H H
C C C C
catalyst surface
Figure 4.1
Schematic view of the catalytic
hydrogenation of an alkyne to an
alkene.
C C
C6H5 CH3
H H
CH C6H5 C 3 + H2
Pd/BaSO4/quinoline
C
again, unfortunately, Z-1-phenylprop-1-ene is not commercially available, so we
have to go still further back and devise a way of making the alkene:
You should already know of a method of making Z-alkenes from alkynes. What
was the procedure?
Addition of hydrogen to an alkyne using Lindlar’s catalyst produces a Z-alkene.
The Z-alkene is obtained because the mechanism of hydrogenation involves the
delivery of both hydrogen atoms from the metal surface to the same side of the
alkyne (Figure 4.1). A poisoned catalyst is used to inhibit the hydrogenation of the
product alkene, thus allowing the alkene to be isolated (Part 1, Section 2.1).
What alkyne should we use to prepare Z-1-phenylprop-1-ene?
1-Phenylpropyne, C6H5C~CCH3.
The equation for the reaction is:
(4.14)
You will be pleased to learn that 1-phenylpropyne is commercially available, so we
have now completed the planning of our synthetic route to pseudoephedrine from a
readily available starting material. The four-stage route is shown in Scheme 4.2
(overleaf).
You may have wondered why we didn’t treat a bromoalcohol with methylamine and
go straight to pseudoephedrine, rather than via the oxirane. This route may well
work, but, because methylamine is basic, it would probably proceed via formation
of an oxirane intermediate anyway. So, simply to keep track of the chemistry, we
shall stick with the present route: isolation of the oxirane, followed by reaction with
methylamine.
Nevertheless, the important message here is that our knowledge of organic reactions,
and in particular their mechanisms, has allowed us to control the way in
which groups are added. We have predicted that the \OH and \
plus its enantiomer
HOBr
C C
HO
C6H5
H
H
Br
CH3NH2
Z-1-phenylprop-1-ene
base C C
HO
C6H5
H
H
NHCH3 4.1
C C
C6H5 CH3
H H
O
CH3 CH3
C C
C6H5 CH3
H H
plus its enantiomer plus its enantiomer
