Chiral 1-azadienes 1 derived from alpha,beta-unsaturated aldehydes and Enders' hydrazines cycloadd to cyclic dienophiles with high facial selectivities. The adducts can be readily converted into enantiomerically pure piperidine derivatives.
Beaudegnies, R., & Ghosez, L. (1994). Asymmetric Diels-alder Reactions With Chiral 1-azadienes. Tetrahedron: Asymmetry, 5(4), 557-560. https://doi.org/10.1016/0957-4166(94)80017-0 (Original work published 1994)