A samarium-promoted cyclopropanation of unmasked
,![](/images/gifchars/beta2.gif)
-unsaturated acids is described. This reaction can be carried out on (
E)- or (
Z)-
,![](/images/gifchars/beta2.gif)
-unsaturated carboxylic acids. In all cases the process is completely stereospecific and stereoselective. A mechanism has been proposedto explain the cyclopropanation reaction.