Cyclopentadienes, when 5,5-disubstituted with electropositive groups, have
considerably enhanced cyclic conjugation in comparison with the parent mole
cule, C5H6. According to various aromaticity indices, 5,5-distannylcyclopen
tadiene is nearly as aromatic as furan. Previous observations on the reacti
vity were interpreted in the light of the observed aromatic stabilization.