Abstract
In explorations of synthesis and chemistry of spiroheterocycles, we found that the reaction of 2-diazopropane with arylidene-benzofuran-2(3H)-one and arylidene-benzofuran-3(2H)-one derivatives generated the spirocyclopropane products. In addition to the expected cycloadducts, an unexpected oxadiazole was formed in some cases. The structures of the obtained adducts have been assigned by means of spectroscopic methods.