Unusual Side Transformation of Spiro[2,4]hepta‐4,6‐dienes into Fulvene Derivatives During Pd‐Catalyzed Cyclopropanation with Diazomethane.

The catalytic cyclopropanation of spiro[2.4]hepta‐4,6‐diene and 1,1,2,2‐tetradeutero‐, 1‐methyl‐, and 1,1‐dimethylspiro[2.4]hepta‐4,6‐dienes on treatment with excess diazomethane in the presence of palladium catalysts, which gives products of double bond dicyclopropanation, is also accompanied by an unusual transformation of the three‐membered ring of the spiro moiety with elimination of the unsubstituted methylene group in the form of ethylene to give the corresponding 5‐methylidenetricyclo[4.1.0.02,4]heptanes (bishomofulvenes). The putative mechanism of the reactions is considered. [ABSTRACT FROM AUTHOR]