The pyrrolidines 2 and 10 were obtained by thermal ene-reactions at +70° and +180° from the (Z)-4-aza-1, 6-diene 1 and from the (E)-4-aza-1, 6-diene 9 in the ratios of 75:25 and 50:50, respectively. On the other hand, these cyclizations proceeded readily in the presence of diethylaluminum chloride at − 78° and − 35° giving in high yield the trans-pyrrolidine 2 from 1 with 100% and from 9 with 89% diastereoselectivity.