Order of reactivity of the following dienes X, Y and Z in Diels–Alder reaction is(X)(Y)(Z)
(a)$X>Z>Y$
(b)$Y>X>Z$
(c)$Y>Z>X$
(d)$X>Y>Z$
Answer
Answer: A ✓ checked by 4AB · confidence medium
Explanation
X (cyclopentadiene) is locked in the s-cis form, so it reacts fastest. Z (isoprene) is a 2-substituted diene: the Me group donates electrons and does not hinder the s-cis conformer. Y, as drawn, is (Z)-1,3-pentadiene (cis-piperylene). In its s-cis conformer the cis terminal Me clashes with the inner H on C1, so very little s-cis form is present and it reacts slowest. Order: X > Z > Y — answer (a).