Acceleration of diels-alder reactions by remote methyl groups
The hexamethyl substituted bismethylenecyclopentane 1a is 4 to 7 times more reactive towards the acetylenic dienophiles 2 and 3 than the nonmethylated 1,2-bismethylenecyclopentane 1b. This unusual consequence of branching is explained in terms of steric and electronic effects.