ORGLIST: Conjugate addition of thiophenols

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From: by way of Joao Aires de Sousa (alihoyer$##$inet.uni-c.dk)
Date: Tue Apr 08 1997 - 13:34:23 EDT


Hello list,

A colleague at work is having serious troble with a conjugate
addition of a thiophenol to an enone. Generally this reaction works
very well, but in her particular instance, it doesn't work under a
variety of basic conditions:
Nucleophile: ortho-mercapto-benzoic acid

The enone has this structure:
4-Pyridyl-CH=CH-CO-(4-Methoxy)-Phenyl.

The desired reaction is a michael addition of the thiol across
the enone. With amines, methoxide, sodium hydride
in
dmf, pyridine and others, mostly unreacted starting material.
With methoxide in methanol a host of products arose, but none of the
desired product (authentic material available for TLC).

I suspect the directing influence of the carbonyl group on the vinyl
group is disturbed by the electron donating methoxy group, as well as
by the electron accepting pyridine ring. Any thoughts on why it
doesn't work under "usual" conditions, or what successful conditions
might be?


Thomas Hoyer
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