W. Adam et al., IMPORTANCE OF STERIC EFFECTS IN THE [4-SUBSTITUTED PENTAMETHYLCYCLOPENTADIENES(2] CYCLOADDITION OF 5), Journal of the Chemical Society, Chemical Communications, (8), 1995, pp. 839-840
Pentamethylcyclopentadienes with a carbon substituent (X = Pr-i, Et, C
H2OH, CHO) at the C-5 position give anti cycloadducts with a variety o
f dienophiles, which establishes the importance of steric effects in t
he [4 + 2] cycloaddition of these plane-nonsymmetric dienes.