Synthesis of Chrysanthemic Acid
Paul F. Schatz University of Wisconsin Madison, Wisconsin 53706
A multistep organic synthesis for undergraduate students
In the intermediate organic chemistry laboratory course at the University of Wisconsin, we wish to acquaint the students, predominately chemistry majors, with the strategies and techniques involved in carrying out a multistep synthesis. This paper describes a synthesis of chrysanthemic acid (I), which has been used successfully in our laboratory course. The overall synthetic route is outlined in eqn. (1)and is based on a synthesis originally reported by Martel and Huynh 11) a t Roussel-Uclaf.
The starting materials, 3-methyl-2-butenoic acid (II), and 2-methyl-3-huten-2-01 (III), are readily available and inexpensive. Moreover, it can be shown that these starting materials can be easily synthesized from acetylene and acetone (eqn. (2)).
1. KOCl
& (111)
hCOgH (1,
( N l
1;: &o,
IkBr g 48% HBr
SO~@N~@ (11
(VI)
(W)
Thus all the carbon atoms of chrysanthemic acid can he traced hack to com~oundscontainine two or three carbon atoms. and this synthesis is an excellentexample of how a struct&ally complicated natural product can he assembled from very simple starting materials. The synthetic plan is convergent which offers advantages other than just thwarting the "arithmetic demon" of linear synthesis ( 1 5 ~ )The . first steps of the synthesis review experimental techniques, such as refluxing, distillation, and recrvstallization, ~reviouslyused in the introductory . organic lah&atory course. The new, more advanced techniques, such as working under an inert atmosphere and high vacuum distillation, are introduced in the later steps. Also,the convergent scheme allows for error (i.e., poor yield or accidental loss of intermediates) without total disaster, since the starting point of any branch of the synthesis is no more than one or two steps away. Finally, the intermediates and products are compatible
Summary of Student Results Reactiond
There are several aspects of the experiment which make it especially suitable for the intermediate or advanced undergraduate chemistrv student. The student's interest in the "~ exprrimtmt is stimulated b y the fact rhvt the s\mth
