Cis, trans diene reacting with trans dienophile in D-A reaction
Macrophage: I thought you did a fine job in analyzing the Diels-Alder reaction of the E,Z-pentadiene with fumaronitrile. To complement my comment above, I offer an illustration of the transition states of the two reactions leading to their respective products. Because fumaronitrile may add with equal facility (mirror image transition states) to either face of the achiral diene, both 2 and 4 are necessarily racemic. "Racemic" transition states represented by 1 are E-endo/Z-exo that afford racemic bis-nitrile 2. Alternatively, "racemic" transition state 3 is E-exo/Z-endo, which leads to bis-nitrile 4 as a racemate.