ORGLIST: Synthesis of Dicyclopropylketone

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From: Dr. Michael Fassbender (mifa$##$nac.ac.za)
Date: Tue Jun 16 1998 - 09:51:01 EDT


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|When I had to synthesize Dicyclopropylketone at the University I
|had to make a 3 stepped synthesis. Please could you tell me how
|the reactions are called from
|a) Gammabutyrolactone to 3-(2-oxolanyliden)gammabutyrolacton via NaOCH3

This type of reaction of alpha-keto esters is known as "Claisen
condensation"; the base OCH3 abstracts a proton in the alpha(3) position of
the lactone to form a nucleophile, which subsequently attacks the carbonyl-C
atom of another ester molecule to form a beta-keto ester (see "Functional
Group Reactions: Carbonyl Condensations" in "Organic Chemistry On line",
http://homework.chem.uic.edu/IEMDL.HTM, a very useful tutorial in this
regard).

|b) 3-(2-oxolanyliden)gammabutyrolacton to 1,8-Dichlorheptan-4-on via HCl

Once the beta-keto ester is formed, it can be easily cleaved by heating in
an acid medium (the so called "decarboxylation") releasing CO2 and yielding
a simple ketone, which would in this case be a
"(1-chloropropyl)cyclopropylketon", considering the chlorination of the
hydroxyl group still left from the cleavage of the first lactone molecule.
Obviously, the cyclopropyl group undergoes an immediate transformation in
the HCl medium, resulting in the formation of 1,7-dichloro heptan-4-one.

|c) 1,8-Dichlorheptan-4-on to Dicyclopropylketon.

In the 1,7-dichloro heptan-4-one molecule there are again two alpha-acid
sites, which undergo a de-protonation when a strong base (BuLi or MeONa) is
present. Since you have now two chlorines at the ends, your dicyclopropyl
ketone is readily obtained via simple nucleophile substitution reaction
(probably S(N)2).

||Thank you

Pleasure; I had to perfom this synthesis in my early studies as well.

Cheers,

------------------------------------------------------
Dr. Michael Fassbender
National Accelerator Centre
P.O. Box 72
7131 Faure
South Africa

Phone: +27-21-843-3820 (business)
            +27-21-855-0056 (private)
Fax: +27-21-843-3901
email: mifa$##$nac.ac.za
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