Quinodimethanes are highly reactive toward dienophiles since Diels-Alder cycloaddn. results in an arom. product. D. functional-based 13C, 1H NMR, NICS, and MO-NICS calcns. indicate that the increase of arom. character of the developing benzenoid ring along the reaction path is esp. pronounced after the transition state is reached, even though the no. of pi orbitals decreases. The forming aliph. ring exhibits large ring current effects during the reaction. [on SciFinder (R)]