Chapter 14, Problem 29P

Furan possesses less aromatic character than benzene as measured by their resonance energies (96 kJ $mo{l}^{-1}$ for furan; 151 kJ $mo{l}^{-1}$ for benzene). What reaction have we studied earlier that shows that furan is less aromatic than benzene and can react in a way characteristic of some dienes?