a-Diazo ketones derived from furanyl-and benzofuranylpropionic acids were prepared, and their rhodium (I1) acetate catalyzed behavior was studied. The results are consistent with a mechanism in which the key step involves addition of a keto carbenoid intermediate on to the furanyl*-bond followed by an electrocyclic ring-opening reaction. In the case of the benzo-substituted furanyl system, the suspected bicyclic intermediate was isolated in high ...